Boston issues curfew to increase coronavirus social distancing The new guidelines recommend staying home between 9 p.m. and 6 a.m.

A global pandemic of the novel coronavirus has now killed at least 10,524 people in the United States.

The U.S. has by far the most cases, with more than 364,000 diagnosed with COVID-19, the disease caused by the new respiratory virus, according to data compiled by the Center for Systems Science and Engineering at Johns Hopkins University.

More than 1.3 million people around the world have been diagnosed with the disease and over 73,900 of them have died. The actual numbers are believed to be much higher due to testing shortages, many unreported cases and suspicions that some governments are hiding the scope of their nations' outbreaks.

Italy has the highest death toll in the world -- more than 16,500.

Monday's biggest developments:

COVID-19 death toll could be lower than expected, CDC chief says

UK Prime Minister Boris Johnson transferred to intensive care

New York state reaches possible apex, death toll reaches 4,758

This will be the 'peak week' for parts of the US, official warns

Here's how the story developed Monday. All times Eastern.

11:57 p.m.: Boston institutes curfew to increase social distancing

Boston Mayor Marty Walsh is recommending a 9 p.m. curfew for residents as coronavirus cases climb in the city.

The new guidelines, which affect all city residents except essential workers, recommend staying at home between the hours of 9 p.m. and 6 a.m.

"That gives people a clear guideline to help them plan their day, make good choices and avoid crowded situations," Walsh said. "We have seen too many unnecessary trips in the evening, and social distancing problems."

Walsh is also asking residents to wear a cloth mask on their face while they are outside their homes, and he has closed all recreational sports facilities in Boston's city parks.

Boston had 259 new COVID-19 cases confirmed on Sunday, the city's largest single-day increase since the pandemic began.

“That’s what a surge looks like and we are still at the beginning of the surge," Walsh said.

As of Sunday, the city had 1,877 total cases and 15 coronavirus-related deaths.

8:51 p.m.: Number of deaths could be lower than expected, CDC chief says

The director of the Centers for Disease Control says that because Americans are heeding social distancing recommendations so well, the number of COVID-19 deaths could be “much, much, much lower” than models have projected.

CDC head Robert Redfield made the remarks to KVOI Radio in Tucson, Arizona.

“If we just social distance, we will see this virus and this outbreak basically decline, decline, decline. And I think that's what you're seeing,” he said. “I think you're going to see the numbers are, in fact, going to be much less than what would have been predicted by the models.”

Redfield’s remarks struck a rosier tone in characterizing the spread of the disease than some of the other health officials in the Trump administration. Earlier in the day, the U.S. Surgeon General equated the coming week’s fallout to the attacks on Pearl Harbor.

Based on models released last week by the White House Coronavirus Task Force, the virus is expected to kill between 100,000 and 240,000 Americans.

7:22 p.m.: NYPD loses another member to coronavirus

The NYPD announced it lost another of its members to the coronavirus on Sunday, as the nation's hardest-hit city continues its battle against the pandemic.

Auxiliary Police Officer Ramon Roman was assigned to the 72nd Precinct in Brooklyn and was a 10-year veteran of the force.

His passing marks the 13th NYPD member to die from the virus since the pandemic began.

As of Monday evening, 1,935 of the NYPD's 38,000 uniformed officers, as well as 293 NYPD civilian employees, have tested positive, according to the department.

NYPD Commissioner Dermot Shea tweeted that 200 members who tested positive have recovered and been cleared to work. That figure includes an officer from a Manhattan precinct who was one of the first to recover.

According to reports, at least two dozen police officers have died from the virus nationwide.

5:32 p.m.: USNS Comfort to treat COVID-19 patients

The Navy ship USNS Comfort, sent to New York City to treat non-coronavirus patients, will now treat those suffering from coronavirus.

New York Gov. Andrew Cuomo said he was informed of the change after speaking with President Trump.

At his afternoon press briefing, Trump confirmed that Cuomo had asked that the ship be reassigned for COVID-19 patients, and that he had approved the change.

The president said the ship will be now treating COVID-19 patients from both New York and neighboring New Jersey.

The ship was originally deployed to New York to handle the overflow of non COVID-19 cases from area hospitals, but there have been only a small number of such cases since the ship arrived.

"This means 1,000 additional beds staffed by federal personnel. This will provide much-needed relief to our over stressed hospital systems," Cuomo tweeted.

5:10 p.m.: First New York City inmate dies from coronavirus

An inmate of a New York City jail is the first detained person in the city to die of the coronavirus, according to the New York City Department of Corrections.

The unnamed inmate died Sunday, 10 days after being admitted to Bellevue Hospital, a department spokesperson said. The department has taken additional steps to prevent the spread of the coronavirus among inmates and corrections employees, including mandating face coverings for everyone in their facilities.

Corrections employees are also given health screenings before they enter a facility, according to the department.

"We continue to follow guidance from national, state, and local public health authorities, and are taking extensive steps every hour of every day to limit the spread of COVID-19 in our facilities," the spokesperson said in a statement.

Nationwide, at least half a dozen federal prison inmates have died from the coronavirus.

3:38 p.m.: UK Prime Minister Boris Johnson taken to intensive care

U.K. Prime Minister Boris Johnson, 55, who was hospitalized Sunday night after contracting the novel coronavirus, has been taken to intensive care after his condition worsened Monday afternoon, according to Downing Street.

Johnson asked Dominic Raab, the secretary of state for foreign affairs, to deputize for him when necessary, Downing Street said.

Earlier Monday, Johnson said he went to the hospital for "some routine tests" as his symptoms persisted.

"I’m in good spirits and keeping in touch with my team, as we work together to fight this virus and keep everyone safe," Johnson tweeted.

A spokesman for the prime minister's office announced in a statement on Sunday night that Johnson had a high fever and was admitted to a London hospital on the advice of his doctor, not in an emergency.

"This is a precautionary step," the spokesman said at the time, "as the prime minister continues to have persistent symptoms of coronavirus ten days after testing positive for the virus."

Tune into ABC at 1 p.m. ET and ABC News Live at 4 p.m. ET every weekday for special coverage of the novel coronavirus with the full ABC News team, including the latest news, context and analysis.

3:10 p.m.: Michigan running 'dangerously low' on personal protective equipment

In Michigan -- one of the states hit hardest by the pandemic -- health care workers are "running dangerously low" on personal protective equipment (PPE), Gov. Gretchen Whitmer warned.

"At Beaumont Hospital, we have less than three days until N95 masks run out. At Henry Ford Health System, we have less than four days. And at the Detroit Medical Center, less than 10 days," Whitmer said Monday. "At all three health systems, there are less than three days until face shields run out and less than six days until surgical gowns run out."

She said that data doesn't include private donations going straight to the hospitals.

Whitmer said state officials are "doing everything we can as the state level to secure more personal protection equipment."

She said FEMA has sent 400 ventilators, 2 million gloves and 1.1 million surgical masks, and plans to ship 1 million more N95 masks this week.

As of Sunday, over 15,000 had tested positive and 617 had died in Michigan.

Eighty percent of the state's cases are in three counties in the Detroit area.

2:50 p.m.: New Jersey sees decline in new case growth rate

New Jersey's death toll from the coronavirus has now climbed to 1,003, Gov. Phil Murphy said Monday.

The Garden State has a total of 41,090 people diagnosed with the virus.

But Murphy tweeted, "we’re seeing a DECLINE in the growth rate of new cases, from 24% day-over-day on March 30th, to roughly 12% today."

"Our efforts #FlattenTheCurve are STARTING TO PAY OFF," he said. "Our job now is to keep flattening it to the point where our day-over-day increase is ZERO."

Murphy stressed, "if we keep up with our current practices, we can get through the peak with the hospital beds that we’re preparing."

But added, "if we relax our social distancing, our health care system will be overrun with a surge FOUR TIMES what it could be. That would be literally disastrous."

"This isn’t over -- not by a long shot," the governor warned.

Murphy said he is signing an executive order to allow retired public employees to return to work without impacting pension status.

2:27 p.m.: Wis. governor suspends in-person voting for Tuesday's primary

Wisconsin Gov. Tony Evers, a Democrat, signed an executive order Monday suspending in-person voting for Tuesday's election, a striking move after the governor resisted taking unilateral action for weeks leading up to the contest. Evers' order calls for moving in-person voting to June 9.

This comes after the Republican-controlled state legislature Monday morning, in a slight to Evers, adjourned a special session he called to make changes to the election.

After Evers' order, the two top Republicans, Wisconsin House Speaker Robin Vos and state Senate Majority Leader Scott Fitzgerald, said they were "immediately challenging this executive order in the Wisconsin state Supreme Court."

1:26 p.m.: Louisiana deaths increase by 38%

In hard-hit Louisiana, statewide deaths jumped 38.3% over the weekend. Louisiana now has a total of 512 fatalities, according to the state's Department of Health.

The number of diagnosed COVID-19 cases made a 44.3% leap over the weekend, now at a total of 10,297 in the state.

Of those hospitalized in Louisiana, 31.1% of the patients are on ventilators, according to the Health Department.

Among the coronavirus-related deaths was a baby girl born prematurely because her mother was on a ventilator and needed oxygen, Dr. William "Beau" Clark of the East Baton Rouge Parish Coroner's Office told ABC News.

It is not clear if the baby was infected with the coronavirus, Dr. Clark said.

Only two of Louisiana's 64 parishes have zero confirmed cases.

"It is absolutely critical that you avoid close contact with others," New Orleans Mayor LaToya Cantrell tweeted Monday.

"It is going to take all of us doing our part and being good neighbors to help flatten the curve and slow the spread," Gov. John Bel Edwards tweeted .

12:32 p.m.: New York state death toll reaches 4,758

In New York -- the state hit hardest by the pandemic -- the death toll has reached 4,758, Gov. Andrew Cuomo said Monday, though he said the rate of death has been "effectively flat for two days."

New York has the highest death toll in the U.S. by far.

More than 130,000 people in New York state have been diagnosed with the coronavirus.

Cuomo said the total number of hospitalizations, ICU admissions and daily intubations are down, which "suggest a possible flattening of the curve."

While New York may have reached the apex of coronavirus infections, the governor added, what happens next "still depends on what we do."

If the state is plateauing, it is because social distancing is working so that must continue, said Cuomo.

Also, the state's health care system "is at maximum capacity today," according to the governor. "The staff cannot work any harder. And staying at this level is problematic."

"There's also a real danger in getting overconfident too quickly. This is an enemy we have underestimated from day one and we have paid the price dearly," Cuomo said.

Schools and non essential businesses will remain closed until April 29, Cuomo said.

Cuomo lectured those who congregated in New York City's squares and parks this weekend and said he's increasing the maximum fine to $1000 for violating the social distancing protocol.

"Now is not the time to be lax. It is a mistake," the governor said.

"If I can't convince you to show discipline for yourself," Cuomo said, then do it for others, like the health care workers "putting their lives on the line."

11:55 a.m.: Another 439 deaths in UK in 24 hours

At least 5,373 patients in the United Kingdom have died from the coronavirus, as of Sunday night. That marks an increase of 439 deaths in 24 hours, according to the Department of Health and Social Care.

Over 51,000 people in the United Kingdom have tested positive for COVID-19, including Prime Minister Boris Johnson and Prince Charles, heir to the British throne.

11:43 a.m.: Masters rescheduled for November

The Masters plans to reschedule 2020's April tournament for Nov. 9 to 15.

"We want to emphasize that our future plans are incumbent upon favorable counsel and direction from health officials," Fred Ridley, chairman of Augusta National Golf Club, said in a statement Monday. "Provided that occurs and we can conduct the 2020 Masters, we intend to invite those professionals and amateurs who would have qualified for our original April date and welcome all existing ticket holders to enjoy the excitement of Masters week."

9:48 a.m.: Spain sees infection rate drop in 'almost all regions'

The novel coronavirus outbreak in Spain appears to be slowing down as the number of new infections drops in "almost all regions," a health ministry official said.

"The growth rate of the pandemic is decreasing in almost all regions," Maria Jose Sierra, with the Spanish Ministry of Health's emergency committee, said in a virtual press briefing Monday.

Sierra cautioned that it will take a few days to "confirm this tendency."

Monday's data from the Spanish health ministry shows that 637 people died from COVID-19 in the past 24 hours -- the lowest daily toll, percentage-wise, since early March -- bringing the nationwide death toll to 13,055. The country also reported 4,273 new cases, bringing the nationwide total to 135,032.

Spain has the second-highest national tally of diagnosed COVID-19 cases in the world, behind the United States, according to a count kept by Johns Hopkins University.

Sierra said around 19,400 health workers in Spain have been infected with the novel coronavirus, accounting for nearly 15% of the total number of cases.

Over the weekend, Spanish Prime Minister Pedro Sanchez announced that he would ask parliament to extend the country's state of emergency by two more weeks, taking the lockdown on mobility until April 26.

"Flattening the curve was our first objective. We’re getting close. But I ask everyone for sacrifice and resistance," Sanchez said in a televised address. "The next objective is to reduce infections even more until the number of new contagions is lower than the number of people recovering each day."

What to know about coronavirus:

How it started and how to protect yourself: Coronavirus explained

What to do if you have symptoms: Coronavirus symptoms

Tracking the spread in the U.S. and worldwide: Coronavirus map

7:18 a.m.: This will be the 'peak week' for parts of the US, official warns

Adm. Brett Giroir, assistant secretary for health at the U.S. Department of Health and Human Services, warned Americans that this will be the "peak week" of the novel coronavirus outbreak for some states and cities.

"For parts of the country, particularly New York, New Jersey, Connecticut, Detroit, this week is going to be the peak week," Giroir told ABC News chief anchor George Stephanopoulos in an interview Monday on "Good Morning America."

"It's going to be the peak hospitalization, peak ICU week and, unfortunately, peak death week," he added. "But that doesn't mean we're over this week. There are other parts of the country that will peak a little bit later, like New Orleans. So we have to be very, very serious about what's happening this week, next week, the following weeks -- do the physical distancing, wear the masks, that's how we're going to defeat this virus."

Giroir, a medical doctor and a key member of the White House coronavirus task force, said the country has "come a long way" in ramping up its COVID-19 testing capacity.

"As of yesterday we've conducted at least 1.67 million tests, and we don't even get information from all of the laboratory-derived tests. These are the ones that are in the hospitals that don't really report up through the system," he said. "We'll do about a million tests this week, and that's plenty enough tests for the people who really need it in the priority groups -- those who are hospitalized, health care workers, elderly."

Giroir said they are also working on scaling up serologic testing, more commonly known as an antibody test, which only requires a drop of blood and sniffs out virus antibodies. The test can't detect whether an individual presently has the virus, but it can tell if they already had it or had been exposed to it at some point in the past because their immune system has developed antibodies to fight it.

"That's very important as we think about reopening the country and the economy," Giroir said, "because if you have had the virus and you have an immune response to it, in all probability you are immune and safe from the virus."

Giroir said he's "very optimistic" that the country will soon have "tens of millions" of serologic tests, potentially by May.

"There are several that are going through the FDA right now," he added.

6:42 a.m.: State of emergency looms in Japan

Japanese Prime Minister Shinzo Abe said he intends to declare a state of emergency over the country's novel coronavirus outbreak amid a recent surge in infections.

During a press conference Monday, Abe said he was making final arrangements for the declaration and would announce it as soon as Tuesday. The order would last for about a month and would apply to seven prefectures that includes major cities such as Tokyo, which has seen a jump in new infections in recent days.

The extent of the emergency measures were not fully known Monday, but the declaration would give prefectural governors the power to ask people to stay home. Local media reports say public transportation and supermarkets would remain open.

As of Monday, at least 3,654 people in Japan have been diagnosed with COVID-19 and 85 of them have died, according to a count kept by Johns Hopkins University.

The Japanese government has admitted that infection routes cannot be traced in an increasing number of cases.

The U.S. Embassy in Tokyo issued a stark warning to Americans in Japan on Friday, saying those who wish to return should do so now or risk being stuck there "for an indefinite period."

"For U.S. citizens now in Japan, if you plan to return to the United States, we recommend that you arrange for an immediate departure. Failure to do so could mean staying abroad for an indefinite period," the embassy said in the alert. "As compared to the number of positive cases and hospitalizations in the United States and Europe, the number of reported COVID-19 cases in Japan remains relatively low. The Japanese Government’s decision to not test broadly makes it difficult to accurately assess the COVID-19 prevalence rate."

3 a.m.: US Forces Japan declares public health emergency

The commander of the United States Forces Japan on Monday announced a public health emergency for the Kanto Plain "due to the steady increase" of novel coronavirus infections in nearby Tokyo.

The declaration, which will remain in effect through May 5, gives commanders the authority to enforce compliance of health protection measures on those who live and work on all U.S. Army, Navy, Air Force and Marine installations and facilities located on the Kanto Plain, the largest lowland in Japan that covers more than half of the eastern Kanto region, including Tokyo.

"Protecting the health and safety of everyone associated with U.S. Forces Japan is my number one priority," Lt. Gen. Kevin Schneider, U.S. Forces Japan commander, said in a statement Monday. "I cannot underscore enough the importance of personal responsibility at a time like this. Stopping the spread of COVID-19 requires the entire team -- service members, civilians, families, and our Japanese partners."

The announcement comes as the daily count of new COVID-19 cases in the Japanese capital have jumped in recent days, from 78 on March 31 to 143 on Sunday, according to data published on the Tokyo Metropolitan Government's website.

Last month, an active duty member of the U.S. Forces Japan tested positive for COVID-19.

In total, 1,033 people have tested positive for the disease in Tokyo and 30 of them have died, according to the government's website. A count kept by Johns Hopkins University show's Japan's nationwide tally is up to 3,654 diagnosed cases and 85 deaths.

ABC News' Aicha El Hammar, Josh Hoyos, Kendall Karson, Rachel Katz, Kelly McCarthy, Terrance Smith, Anthony Trotter and Lucien Bruggeman contributed to this report.