U.S. President Donald Trump announced Friday that he is declaring the coronavirus pandemic a national emergency, as Washington struggles with providing Americans with relief and officials race to slow the spread of the outbreak.

Speaking from the White House, Trump said, "I am officially declaring a national emergency," unleashing as much as $50 billion US for state and local governments to respond to the outbreak.

Trump also announced a range of executive actions, including a new public-private partnership to expand coronavirus testing capabilities with drive-through locations, as his administration has come under fire for being too slow in making the test available.

Later in the day, House Speaker Nancy Pelosi announced a deal with the Trump administration for an aid package from Congress that would provide free tests, sick pay for workers and bolster food programs.

"We are proud to have reached an agreement with the Administration to resolve outstanding challenges, and now will soon pass the Families First Coronavirus Response Act," Pelosi announced in a letter to colleagues. The House was poised to vote.

House Speaker Nancy Pelosi updates reporters Friday about talks on the federal aid package. (J. Scott Applewhite/The Associated Press)

Access to testing has been a persistent source of concern. Still, Trump said that officials don't want people taking the test unless they have certain symptoms. "We don't want people without symptoms to go and do that test," Trump said, adding, "It's totally unnecessary."

He also denied responsibility for the slow rollout of testing. "I don't take responsibility at all," Trump said.

Trump took a number of other actions to bolster energy markets, ease the financial burden for Americans with student loans and give medical professionals additional "flexibility" in treating patients during the public health crisis.

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He waived interest on federally held student loans and moved to prop up energy markets by directing the Department of Energy to buy oil to fill the strategic petroleum reserve "right up to the top."

"Through a very collective action and shared sacrifice, national determination, we will overcome the threat of the virus," Trump said.

Declaration welcomed

The White House is under enormous pressure, dealing with the crisis on multiple fronts as it encroached ever closer on the president.

The virus has swept in alarming ways across American life, sending the financial markets into a dangerous slide and shuttering schools and sporting events and limiting everyday interactions in communities across the country.

And a personal health scare intensified as White House officials worked to determine the level of exposure by the president and senior aides to several foreign officials who have since tested positive for the virus.

A sign informs visitors that Space Needle is closed on Friday in Seattle. (Ted S. Warren/Associated Press)

Trump said he was gratified that Brazilian President Jair Bolsonaro tested negative for the virus, after the pair sat next to each other for an extended period last weekend. A senior aide to Bolsonaro tested positive. "We have no symptoms whatsoever," said Trump, who has not gotten tested for the virus or taken steps to self-isolate.

Hospitals welcomed Trump's emergency declaration, which they and lawmakers in Congress had been requesting. It allows the Health and Human Services Department to temporarily waive certain federal rules that can make it harder for hospitals and other health-care facilities to respond to an emergency.

Such rules include a Medicare requirement that a patient spend three days in the hospital before the program will pay for care in a nursing facility. Waiving the rule would make more inpatient beds available. Another rule requires doctors and other clinicians to be licensed in the state in which they are providing services. It can be waived if the physician is licensed in another state.

The American Medical Association said the emergency declaration would help ensure the health-care system has sufficient resources to properly respond to the ongoing outbreak.

Traders listen at the New York Stock Exchange to Trump's televised speech from the White House on Friday. (Mark Lennihan/Associated Press)

Trump's actions were also viewed favourably on Wall Street, sending the Dow Jones Industrial Average up 1,985 points, or 9.4 per cent, its best gain since October 2008. Stocks doubled their gains in the last half-hour of trading as Trump made his remarks.

For most people, the coronavirus causes only mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia.

The vast majority of people recover. According to the World Health Organization, people with mild illness recover in about two weeks, while those with more severe illness may take three to six weeks.

Providing sick pay for workers is a crucial element of federal efforts to stop the rapid spread of the infection. Officials warn that the nation's health-care system could quickly become overwhelmed with gravely sick patients, as suddenly happened in Italy, one of the countries hardest hit by the virus.

The ability to ensure paycheques will keep flowing — for people who stay home as a preventative measure or because they're feeling ill or caring for others — can help assure Americans they will not fall into financial hardship.

A volunteer checks their mask at a drive-through COVID-19 testing site in Colorado Springs, Colo., on Friday. (Chancey Bush/The Gazette via AP)

A deal between Congress and the White House would cap a tumultuous week in which Washington strained for a comprehensive response to an outbreak that is testing the nation's political, financial and health-care systems.

Trump has struggled to show he's on top of the crisis, after giving conflicting descriptions of what the U.S. is doing to combat the virus.

The House aid package builds on an emergency $8.3 billion US measure approved last week.

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Pelosi promised a third coronavirus package will follow soon, though the House is leaving Washington on Friday for a previously scheduled recess. That measure will include more aggressive steps to boost the U.S. economy, which economists fear has already slipped into recession.

But there's little appetite within either party for Trump's proposal to suspend collection of the 6.2 per cent Social Security payroll tax. States are already clamouring for fiscal relief from Washington as the virus threatens their budgets.