SEATTLE — The U.S. death toll from the coronavirus rose to six on Monday, and patients were being treated in at least 15 states, deepening fears about the outbreak's rapid spread and the medical, psychological and economic toll it will exact on the United States.

Four deaths announced Monday and two others this weekend all occurred in Washington state, the center of the nation’s most serious outbreak. Eight of the state’s 18 cases, as well as four of the deaths, are linked to the Life Care Center nursing home in Kirkland, Wash., and at least 50 other residents and staff members have reported coronavirus-like symptoms. King County leaders declared a state of emergency, and health officials said they are trying to figure out how far the outbreak has expanded into surrounding counties.

Nationwide, the number of cases topped 100, and U.S. officials used increasingly dire language, even as they sought to push back against waves of panic and misinformation online.

“We know there will be more cases,” Vice President Pence said at a White House news conference. “Now we’re focused on mitigation of the spread as well as treatment of people that are affected.”

Trump administration officials stressed Monday that the risk posed to the public by the coronavirus remains low but cautioned the outbreak could change course as the disease spreads through person-to-person contact.

Arizona, California, Florida, Georgia, Illinois, Massachusetts, Nebraska, New Hampshire, New York, Oregon, Rhode Island, Texas, Utah, Wisconsin and Washington state either have cases confirmed by health officials or have been treating patients with coronavirus-like symptoms.

Late Monday, Georgia health officials said two people, a couple living in Atlanta, tested positive for coronavirus after one of them returned from a trip to Italy.

Meanwhile, U.S. lawmakers negotiated through the weekend on an emergency spending bill and were closing in Monday on a $7.5 billion coronavirus package, said two people familiar with the negotiations who spoke on the condition of anonymity to discuss the proceedings.

The figure being negotiated on Capitol Hill dwarfs the $1.25 billion request the White House sent Congress last week. The legislation is likely to be unveiled on Tuesday and pass the House later this week before moving on to the Senate.

At a meeting with leaders of the world’s largest pharmaceutical companies, President Trump hinted he may enact new travel restrictions on unnamed nations with large outbreaks and touted his administration’s steps to fight the virus.

The president listened and occasionally interjected to press pharmaceutical executives on how quickly a vaccine and treatments could be developed. Therapeutic human trials could begin as early as April, but a vaccine would take roughly 12 to 18 months to develop, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

Asked about the state of the economy after a tumultuous week for the stock markets, the president noted that “the market’s up today,” insisting that “our country’s very strong economically.” But he said that he would like to see the Federal Reserve do more to address the financial challenges posed by the coronavirus’s spread.

A motel for the sick

Around the same time on Monday, bleary-eyed public health officials in Washington state held a news conference, saying they were working around the clock to find places to house the ill. They said King County is in final negotiations to buy a motel to isolate the ill and hopes to make new housing available this week.

County hotlines were ringing off the hook, they said. And the outbreak was taxing hospitals, physicians and other health-care workers on the front lines.

King County Executive Dow Constantine said the outbreak had entered “a new stage.” The county’s new emergency declaration, he said, will allow him to authorize overtime for county officials and quickly set up the modular housing, which could serve 100 to 200 people.

King County now has 14 confirmed cases, including those who have died, while neighboring Snohomish County has four. Local officials said they were not recommending closing schools.

“We expect the number of cases will continue to increase in the coming days and weeks, and we’re taking this situation extremely seriously,” said Jeff Duchin, health officer for Seattle and King County. “The risk for all of us of becoming infected will be increasing.”

Duchin urged people to take basic precautions, such as washing their hands frequently and staying home if they are sick. He said eventually there will be so many cases — most of them mild — that it will be impossible to track them individually.

“We’re going to see a lot of sick people, and we’re going to have a tremendous challenge on our health-care system,” he said, adding that “it’s impossible for me to predict what the peak of this outbreak will be. And everything we’re doing now that is trying to blunt that peak.

Texas officials lambaste CDC

In Texas, San Antonio lambasted the Centers for Disease Control and Prevention after the agency released a woman who later was found to have the novel coronavirus. The city unsuccessfully sought a temporary restraining order to prevent the release of dozens of people scheduled to leave quarantine in the San Antonio area and demanded another round of tests be performed.

San Antonio Mayor Ron Nirenberg noted that the released woman had visited a mall, eaten at the food court and stayed at the Holiday Inn Express near the city’s airport. The woman arrived in Texas last month from Wuhan, China, and was part of a 91-person group evacuated from Asia. She had not shown symptoms and tested negative in two tests, officials said. After she was let go, the CDC obtained the results of a third test showing a “weakly positive” confirmation of the virus.

“We simply cannot have a screw-up like this from our federal partners,” said Nirenberg. For days, local officials have fumed over the federal government’s lack of response to concerns about transporting quarantined patients to the area. They have also called for better protocols to prevent local transmission.

Nationwide, signs of spreading panic included the stockpiling of food, sanitizers and cleaning supplies.

At the Trader Joe’s in Mountain View, Calif., the freezer sections were empty of pizza and most ready-made meals. There was no pasta or rice. Across town at the Costco near Google’s headquarters, customers climbed shelves to reach groceries, and lines snaked through the aisles.

A Whole Foods employee in Los Altos, Calif., said the store was out of “pasta, beans, frozen vegetables, hand sanitizer, toilet paper, paper towels. “I’ve worked here 10 years, and I’ve never seen anything like this,” she said.

Health officials continued to beg Americans to stop buying masks and save them for health workers who truly need them. On cable news, U.S. Surgeon General Jerome Adams argued that consumers who buy masks “actually can increase the spread of coronavirus” because people who wear them improperly tend to fidget with their masks and touch their faces repeatedly.

Online, Amazon shoppers in Seattle, San Francisco, New York and Washington also ran into problems, with the company warning customers that its same-day grocery-delivery service “may be limited” amid reports of consumers stocking up.

The company routinely offers two-hour windows for delivery of items, but the rush by shoppers on Monday left few delivery spots for the next two days. (Amazon chief executive Jeff Bezos owns The Washington Post.)

Chaos abroad

Meanwhile, worsening situations in various countries overseas offered possible signs of what may lie ahead for the United States.

Schools across Japan mostly closed their doors Monday in response to a controversial request by Prime Minister Shinzo Abe last week to make a concerted attempt to slow the spread of the virus.

South Korea said it would extend its school closures by two weeks to March 23, its education minister announced.

Japanese officials studying the outbreak on the Diamond Princess cruise ship said more than half of those infected — nealy 400 out of 705 people who tested positive — showed no symptoms, underscoring just how difficult the virus is to detect and how many people may have contracted it without knowing it. Some would never have been tested unless they had been onboard the ship, they said. While many people appear able to shrug off the virus, it clearly is devastating to the elderly and people with underlying health problems. At least seven of the cruise ship passengers died.

The European Union’s internal market commissioner said Monday the coronavirus has led to about $1.1 billion in losses per month for the European tourism industry since the start of 2020. And British Airways on Monday said it was canceling hundreds of flights — including a dozen between London and New York — in response to the coronavirus outbreak.

An adviser to Iran’s supreme leader died after contracting the coronavirus, state media reported Monday. Iraq and Egypt confirmed more cases, many of them linked to Iran.

Senegal confirmed its first case, marking the second case found in sub-Saharan Africa. Global health officials have expressed strong worries that the epidemic and death toll could grow rapidly if it reaches areas such as Africa, which in many places lacks the resources and the health infrastructure to combat the virus. Nigeria, the continent’s most populous country and biggest economy, announced last week that doctors had diagnosed the illness in a businessman from Italy.

Jay Greene in Seattle; Danielle Paquette and Borso Tall in Dakar, Senegal; Christina Passariello in San Francisco; James McAuley in Paris; Simon Denyer in Tokyo; Erin Cunningham in Istanbul; and Kim Bellware, Katie Mettler, Lenny Bernstein Lena H. Sun and Teo Armus in Washington contributed to this report.