Washington state, home of the nation's first confirmed infection, has seen eight confirmed cases, including the nation's first death from the virus this weekend.

State and local authorities stepped up testing for the illness as the number of new cases grew nationwide, with new infections announced in California, Illinois, Rhode Island, New York and Washington state. Authorities in the Seattle area said two more people had been diagnosed with the COVID-19 virus, both men in their 60s who were in critical condition, and two health care workers in California were also diagnosed.

A man in his 50s died in Washington on Saturday, and health officials said 50 more people in a nursing facility in Kirkland, Washington, are sick and being tested for the virus. On Sunday night, the International Association of Fire Fighters said 25 members who responded to calls for help at the nursing facility are being quarantined.

The first U.S. case was a Washington state man who had visited China, where the virus first emerged, but several recent cases in the U.S. have had no known connection to travelers.

In California, two health care workers in the San Francisco Bay area who cared for an earlier coronavirus patient were diagnosed with the virus on Sunday, the Alameda and Solano counties said in a joint statement.

The health care workers are both employed at NorthBay VacaValley Hospital in Vacaville, California, and had exposure to a patient treated there before being transferred to UC Davis Medical Center in Sacramento, the statement said. That patient was the first person in the U.S. discovered to have contracted the coronavirus with no known overseas travel.

Alameda County declared a state of emergency on Sunday following the news.

Elsewhere, authorities announced Sunday a third case in Illinois and Rhode Island and New York's first cases as worried Americans swarmed stores to stock up on basic goods such as bottled water, canned foods and toilet paper.

The hospitalized patient in Rhode Island is a man in his 40s who had traveled to Italy in February. New York confirmed Sunday that a woman in her late 30s contracted the virus while traveling in Iran. The patient is not in serious condition. She has respiratory symptoms and has been in a controlled situation since arriving in New York, according to a statement from the governor's office.

As the fallout continued, Vice President Mike Pence and Health and Human Services Secretary Alex Azar sought to reassure the American public that the federal government is working to make sure state and local authorities are able to test for the virus. Both said during a round of TV talk show appearances Sunday that thousands more testing kits had been distributed to state and local officials, with thousands more to come.

"They should know we have the best public health system in the world looking out for them," Azar said, adding that additional cases will be reported and the overall risk to Americans is low.

As the cases ticked up, some Americans stocked up on basic supplies — particularly in areas with diagnosed cases — and began to take note of the impact on daily life. Stores such as Costco sold out of toilet paper, bottled water and hand sanitizer outside Portland, Oregon, where a case was announced Friday. Sports games and practices were canceled into the coming school week. Some churches said they would not offer communion because of fears of viral spread.

As Americans prepared, researchers at the Fred Hutchinson Cancer Research Center and the University of Washington on Sunday said they had evidence the virus may have been circulating in the state for up to six weeks undetected — a finding that, if true, could mean hundreds of undiagnosed cases in the area. They posted their research online, but it was not published in a scientific journal or reviewed by other scientists.

Trevor Bedford, an associate professor who announced the preliminary findings on the virus in Washington state, said on Twitter late Saturday that genetic similarities between the state's first case on Jan. 20 and a case announced Friday indicated the newer case may have descended from the earlier one. The Jan. 20 case was the first known case in the U.S.

"I believe we're facing an already substantial outbreak in Washington State that was not detected until now due to narrow case definition requiring direct travel to China," he said on Twitter.

Bedford did not immediately reply to an e-mail requesting an interview Sunday.

Scientists not affiliated with the research said the results did not necessarily surprise them and pointed out that for many people — especially younger, healthier ones — the symptoms are not much worse than a flu or bad cold.

"We think that this has a pretty high rate of mild symptoms and can be asymptomatic. The symptoms are pretty non-specific and testing criteria has been pretty strict, so those combinations of factors means that it easily could have been circulating for a bit without us knowing," said Justin Lessler, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

Dr. Adam Lauring of University of Michigan called the findings "high quality work" from scientists who've done similar work with the flu virus for years.

"They show their data and they show their work," Lauring said. "It's more than a series of tweets" because the researchers back up what they found with data that they've shared online. "If there's something wrong, someone will find it."

Dr. Carlos del Rio of Emory University School of Medicine said the findings are from respected researchers in genomic sequencing and they make sense because of the geographic proximity of the two cases.

"This is a good time to reinforce the things we all should be doing to stop the spread of flu. Wash your hands. Don't touch your face. If you have a cold, stay home ... It's a good time to remind ourselves of that," he said.

Pence, named by the president to be the point-person overseeing the government's response, said more than 15,000 virus testing kits had been released over the weekend. And, the administration is working with a commercial provider to distribute 50,000 more, he said.

The vice president said testing was among the first issues raised by governors he's spoken with so far. Several states have begun their own testing, including Washington state, Oregon and Illinois.

"We're leaning into it," Pence said.

Azar said more than 3,600 people already have been tested for coronavirus and the capability exists to test 75,000 people. He forecast a "radical expansion of that" in the coming weeks.

Pence and Azar spoke a day after President Donald Trump approved new restrictions on international travel to prevent the spread within the U.S. of the new virus, which originated in China. There are now more than 80,000 cases worldwide and about 3,000 deaths.

Two Americans are now known to have died of the virus, one in Washington state and one in China.

The new U.S. travel restrictions apply to Iran, although travel there by Americans already is severely limited, as well as heavily affected regions of Italy and South Korea. Trump tweeted Sunday that any travelers from those countries will be screened when they arrive in the U.S.

The number of known coronavirus cases in the U.S. had reached76 as of Sunday, counting people evacuated from a cruise ship and the city of Wuhan in China.

Trump said Saturday at a White House news conference that he was thinking about closing the southern border with Mexico as a precaution. Azar said Sunday that Mexico has few coronavirus cases and that it would take a dramatic change in the circumstances there to prompt serious consideration of a border shutdown.

The president, Azar said, "was trying to say everything's on the table."

"We will take whatever measures are appropriate and necessary to protect the American people, but we don't forecast doing that any time soon," he said of closing the border.

Pence noted that an infectious disease expert is joining an existing White House coronavirus task force on Monday. Last week, Pence announced the addition of Debbie Birx, a State Department ambassador-at-large and medical doctor who is the administration's global HIV/AIDS response coordinator, to the virus panel.

Despite calls by Trump and Pence for political unity in the face of the viral threat, the issue has become mired in the partisan rancor in Washington, with both Republicans and Democrats accusing each other of mining the issue for political gain.

Trump, at a political rally last week, accused Democrats of "politicizing" the issue and said their criticism of his handling of the public health challenge was their new "hoax."

At the White House on Saturday, Trump said he was not trying to minimize the threat from the virus.

"Again, the hoax was used in respect to Democrats and what they were saying," he said Saturday.

Democratic presidential candidate Joe Biden, who emerged victorious Saturday night from South Carolina's primary, criticized the administration over the availability of testing kits.

Biden also panned the administration's decision to have political appointees Pence and Azar, neither of whom are scientists by training, appear on the Sunday shows, instead of an expert like Dr. Anthony Fauci, the National Institutes of Health infectious disease chief.

Biden claimed the administration doesn't have testing kits. Pence and Azar said thousands of kits had been distributed.

Azar said he didn't know what Biden was talking about when the former vice president said testing kits didn't exist. Azar said the Centers for Disease Control and Prevention had developed a lab test for coronavirus with "historic speed."

Pence was interviewed on CNN's "State of the Union" and Azar commented on "Fox News Sunday," CBS' "Face the Nation" and ABC's "This Week." Biden commented on CNN.