Key updates on the coronavirus outbreak:

Bay Area: San Francisco Mayor London Breed declares an emergency, Contra Costa County reports two cases, major company pulls out of SF’s Game Developers Conference.

California: 8,400 people in the state are now self-quarantined.

Nationwide: CDC warns Americans to prepare for the virus to become more widespread.

Breaking news developments on Feb. 25, 2020:

5:03 p.m.: Top California health official releases video statement: Dr. Sonia Angell, director of the California Department of Public Health, says the virus is expected to spread in the state and advises people to take same precautions they would to avoid getting the flu.

1:45 p.m. SF declares state of emergency: Mayor London Breed issued a state of emergency for San Francisco on Tuesday, a move that will allow the city to add resources to contain the virus in case the city experiences an outbreak. San Francisco officials are urging schools to begin drafting plans for closures and businesses to consider their work-from-home policies should employees need to self-quarantine. Currently one coronavirus patient, who was on the Diamond Princess cruise ship in Japan before evacuating to Travis Air Force Base, being treated in San Francisco.

11:50 a.m. California home quarantine numbers rise again: The California Department of Public Health says 8,400 people are now self-quarantined. That’s an increase from 8,000 yesterday.

11:35 a.m.: SF mayor plans announcement: San Francisco Mayor London Breed announced that she, along with health and emergency management officials, planned to provide an update on "the city's preparedness efforts" around coronavirus at 1:45 p.m.

11:21 a.m. Markets dive again: Both the Dow and the S&P 500 fell close to 3% in late-morning trading, following the CDC’s announcement that Americans should prepare for the coronavirus to potentially spread in their communities. Shares in local chipmakers AMD, Intel and Nvidia once again fell more than the overall market. The drops follow a day of heavy losses on Monday, especially for tech stocks.

10:42 a.m. Two cases in Contra Costa: Two people with coronavirus are being treated at Contra Costa County hospitals, county health officials said Tuesday. They were transferred from Travis Air Force base in Fairfield, which is housing passengers from the disease-stricken cruise ship Diamond Princess in Japan. The patients are not showing symptoms.

10:31 a.m. United sees plunge in passengers for Asia flights: United Airlines, the biggest carrier at SFO, says demand for its trans-Pacific routes have dropped 75% — and that’s on top of already-canceled flights to China. United continues to fly from SFO to South Korea, a country so hard-hit by the virus that the U.S. is recommending against travel there, but the airline is offering waivers for refunds if passengers want to cancel.

8:56 a.m. CDC says Americans should prepare for virus: With coronavirus now spreading community-wide in multiple countries, including parts of Europe, the Centers for Disease Control and Prevention says the world is on the cusp of a pandemic and advises that Americans begin preparing now for the virus to circulate here. “Ultimately we expect we will see community spread in this country,” said Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases with the CDC. “It’s not a question of if, but when, and how many people in this country will have severe illness.” She said the world was “closer to definition of pandemic.”

8:55 a.m. Electronic Arts pulls out of SF’s Game Developers Conference: Redwood City video game maker Electronic Arts became the latest company to pull out of the Game Developers Conference scheduled for next month in San Francisco. EA is one of the largest video game companies, so the move is a significant blow to the conference, which has already lost Facebook and PlayStation. Reports of new cases of the virus around the world contributed to EA’s decision, according to company spokesman John Reseburg.“We have decided to take additional steps to protect the well-being of our employees including the restriction of all non-essential travel,” Reseburg wrote in an email. “As a result, we are also canceling our official participation at GDC and limiting attendance to other events.”

6:40 a.m. Markets stabilize: After heavy losses Monday sparked by investor concerns over the coronavirus, the Dow Jones Industrial Average and the S&P 500 were both up slightly in early trading Tuesday. Several major Bay Area tech stocks, which took a beating on Monday, also opened roughly level.

Updates from Monday, Feb. 24

7:26 p.m. The number of confirmed coronavirus cases in the U.S. jumped to 53 on Monday after more passengers from the Diamond Princess cruise ship who were evacuated into the U.S. tested positive.

6:19 p.m. South Korea saw its coronavirus cases nearly double in two days to 833. Italy now has more cases (229) than Japan (159). Worldwide, there are 80,078 cases as of Monday evening, and 2,699 deaths.

6:14 p.m. A judge has temporarily blocked a plan to house patients who have tested positive for the coronavirus but don’t require hospitalization at a site in Costa Mesa (Orange County).

12:29 p.m. More cruise ship passengers positive: Three additional cruise ship passengers were moved from Travis Air Force Base to Solano County hospitals Sunday after testing confirmed they have the coronavirus, according to Scott Pauley of the Centers for Disease Control and Prevention. They were asymptomatic. 15 cruise ship passengers have now tested positive for coronavirus — either by testing in Japan or the CDC — and 3 are awaiting test results.

12:08 p.m. 8,000 in California now self-quarantined: Some 8,000 people across the state have quarantined themselves, the California Department of Public Health told The Chronicle. That’s up from 6,700 last week. The federal government has asked people who returned from China, which has the highest number of coronavirus cases, to stay home from work and avoid big crowds.

11:38 a.m. Pelosi visits Chinatown: House Speaker Nancy Pelosi is touring Chinatown to assure people that it’s safe to visit despite the coronavirus. She visited the Tin How Temple, followed by the Golden Gate Fortune Cookie Factory, whose owner Kevin Chan, says his business and others are down 70%.

10:52 a.m. RSA Conference opens despite pullouts: The RSA Conference, a major cybersecurity event, opened Monday in San Francisco’s Moscone Center despite the pullouts of several major companies — Verizon, AT&T Cybersecurity and IBM — over coronavirus fears. Signs urging caution about health greeted attendees, who are being encouraged to clean their hands often and avoid touching their nose and mouth. Conference organizers also cautioned against having contact with anyone with cold or flu-like symptoms, which can be signs of the virus.

8:39 a.m. Another pullout from SF’s Game Developers Conference: Japanese video game designer Hideo Kojima’s production company announced Monday it would no longer attend the Game Developer Conference slated to take place in San Francisco next month. “Kojima Productions has made the difficult decision to cancel our participation at the 2020 Game Developers Conference due to increasing concerns related to coronavirus,” the company wrote on Twitter Monday.

8:10 a.m. Markets plunge: U.S. stocks fell sharply in early trading Monday, following a broad sell-off overseas, as a surge in coronavirus cases and a worrisome spread of the disease outside the epicenter in China sent investors running for safety. Technology companies were among the worst hit by the sell-off. Apple, which depends on China for a lot of business, slid over 4%. Microsoft slumped over 3%. Banks, including JPMorgan Chase and Bank of America, were also big losers.

Updates from Saturday, Feb. 22

5:45 p.m. Global cases still climbing, spiking outside China: South Korea is now reporting 433 cases of the new virus, a concerning rise that indicates the illness is spreading in parts of the community now, public health officials said. Worldwide, there are 78,630 cases as of Saturday evening, and 2,460 deaths.

12:42 p.m. Judge blocks evacuee transfer from Travis to Orange County: Around 50 people quarantined with potential coronavirus at Travis Air Force Base in Fairfield were temporarily blocked from being transferred to Fairfield Developmental Center in Costa Mesa. A federal judge ruled in favor of Costa Mesa officials, who said the Fairview Center was dilapidated and lacked security measures to ensure a quarantine.

Updates from Friday, Feb. 21

3:42 p.m. Signs of community illness outside China: Cases are surging in several Asian countries outside China, including South Korea, Japan, Singapore and Thailand, raising concerns among U.S. health officials that the new coronavirus is spreading from person to person in communities there. The climbing case counts triggered a new State Department advisory that Americans avoid travel by cruise ship in East Asia.

1:21 p.m. Port of Oakland sees fewer ships: While January cargo volumes were strong, the Port of Oakland expects 30 fewer ships with routes to Asia through spring, according to spokesman Mike Zampa. The port saw 118 total ships in January, according to Zampa, who said “there could be impacts ahead.”

12:42 p.m. For cruise evacuees at Travis, the ordeal continues: “Anything that can go wrong in this nightmare has gone wrong,” a Redwood City resident, whose husband has tested positive for the coronavirus, told The Chronicle from her room at Travis Air Force Base in Fairfield, where she is quarantined after being evacuated from the Diamond Princess cruise ship. Her husband has been taken to a San Francisco hospital.

11:41 a.m. Sacramento County resident tests positive: A second Northern California resident has tested positive for the new virus this week, public health officials said. The case reported Friday is in a Sacramento County resident who had recently returned from China. The day before, Humboldt County reported its first case, also in a person who was exposed to the virus in China.

11:02 a.m. Third sponsor quits RSA Conference: Verizon informed organizers it was dropping out of next week’s RSA Conference in San Francisco. It is the third large sponsor after IBM and AT&T to withdraw over coronavirus concerns. Mayor London Breed sent a letter to attendees informing them that the coronavirus “is not circulating in our community” and urging them to “prevent fears, rumors and misinformation from guiding our actions.”

10:23 a.m. 34 diagnosed with coronavirus in the U.S.: The Centers for Disease Control and Prevention said there are now 34 confirmed cases in the United States, including 18 evacuees from the Diamond Princess cruise ship who have tested positive and three people repatriated from Wuhan, the epicenter of the outbreak in China. Several Americans still hospitalized in Japan are seriously ill.

Updates from Thursday, Feb. 20

5:34 p.m. coronavirus case in Humboldt County: A person in Humboldt County has tested positive for the new virus, public health officials said. A second person who has been in close contact with the individual and who has symptoms of illness is also being tested.

Both individuals are in isolation in their own home. Other close contacts identified by public health officials will be instructed to quarantine themselves at home and will be monitored for symptoms.

The case is the first in Humboldt County. There have been eight other cases confirmed in California, plus several individuals who tested positive for the virus while overseas and are currently being retested by the Centers for Disease Control and Prevention.

4:03 p.m. Virus patient from cruise ship at SF hospital: A person with coronavirus is being treated at a San Francisco hospital, city health officials said Thursday. They declined to specify which hospital. The person has no symptoms but tested positive for the virus in Japan, and was brought to San Francisco from Travis Air Force Base in Fairfield, where passengers from the Diamond Princess were being quarantined. The patient is the third person with coronavirus to be treated at a San Francisco hospital. Two previous patients, a couple from San Benito County, were treated at UCSF and released last week in good health.

3:01 p.m. 16 cruise evacuees from Travis taken to hospitals: At least 22 more people evacuated from the Diamond Princess cruise ship in Japan to two U.S. air bases have either tested positive or showed coronavirus symptoms, including 16 who arrived at Travis Air Force Base but have now been transported to local hospitals, a spokesman for the Centers for Disease Control and Prevention told The Chronicle. At least six passengers who arrived at Lackland Air Force base near San Antonio have also been taken to hospitals for further testing, he said.

2:50 p.m. Santa Clara patient recovered: Santa Clara County’s health department announced “that the first confirmed case of novel coronavirus in Santa Clara County has fully recovered and has been released from isolation. He was never sick enough to be hospitalized. He isolated at home and was monitored by public health staff for the duration of his isolation. ... Currently, there is no evidence that novel coronavirus is circulating in Santa Clara County and risk remains low.”

2:10 p.m. PlayStation pulls out of Game Developers Conference: “We have made the difficult decision to cancel our participation in Game Developers Conference due to increasing concerns related to COVID-19 (also known as coronavirus),” a spokeswoman said in a statement. “We felt this was the best option as the situation related to the virus and global travel restrictions are changing daily. We are disappointed to cancel our participation, but the health and safety of our global workforce is our highest concern. We look forward to participating in GDC in the future.”

1:41 p.m. Facebook withdraws from Game Developers Conference in SF: Facebook said in a blog post that it would not attend the conference, a major gaming industry convention March 16-20, due to coronavirus concerns. “The health of our employees and the wider games community comes before anything else,” the company said.

12:58 p.m. AT&T pulls out of SF conference: AT&T will no longer attend the RSA Conference, a major cybersecurity event at San Francisco’s Moscone Center next week, due to coronavirus concerns. “We understand and respect their decision,” a bulletin on the conference website read, noting that cancellations represent a minimal number of attendees. The conference opens on Monday.

11:18 a.m. Rest of Wuhan evacuees released from Travis: All 53 remaining evacuees from Wuhan who were quarantined at Travis Air Force Base after taking a U.S. government-chartered flight home have been released. “All of these individuals have been medically cleared and CDC officials have lifted their quarantine orders,” the Centers for Disease Control and Prevention said Thursday. Travis continues to house evacuees from the virus-stricken Diamond Princess cruise ship.

10:45 a.m. Pandemic could inflict huge cost to economy, report says: If the coronavirus morphs into a global pandemic, global GDP for 2020 would drop by $1.1 trillion, or 1.3% of previous forecasts, and send the U.S. into recession, according to economic forecasting agency Oxford Economics. If a pandemic were limited to Asia, global GDP could dip by $400 billion, or 0.5% below expectations.

7:00 a.m. Nearly 7,000 travelers in CA asked to monitor, isolate themselves: Federal officials suggested to more than 6,700 travelers who have returned to California after Feb. 2 from China, outside of Hubei Province, to “monitor their health, stay home and limit interactions with others as much as possible,” California Department of Public Health officials said.