The coronavirus may have been circulating for weeks undetected in Washington state.

Seattle — The coronavirus may have been circulating for weeks undetected in Washington state, a preliminary finding that could mean hundreds of undiagnosed cases in the state that’s also home to the nation’s first confirmed infection and now the first death, researchers said Sunday after analyzing genetic samples of the pathogens.

Health officials in Washington state said Sunday night that a second person had died from the coronavirus.

State and local authorities stepped up testing for the illness as the number of new cases grew nationwide, with new infections announced in Illinois, Rhode Island 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. Those cases brought the numbers to six in Seattle.

A man in his 50s died in Washington on Saturday and health officials said 50 more people in a nursing facility in Kirkland, Wash., are sick and being tested for the virus.

Elsewhere, authorities announced Sunday a third case in Illinois and Rhode Island’s first case 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.

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 COVID-19. 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 Americans prepared, researchers at the Fred Hutchinson Cancer Research Center and the University of Washington on Sunday said they had evidence that COVID-19 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. The research 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 email 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 associated professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

“And that was what a lot of us was thinking was likely.”

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 88,000 cases worldwide and at least 3,000 deaths, mostly in China.

Three Americans are now known to have died of the virus, two 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.