Health officials in Washington state say a second person infected with the coronavirus has died there, while New York's governor says his state has confirmed its first case of the illness.
The Washington death was in the Seattle area and was reported on the website of the Seattle and King County public health department.
On Saturday, the same officials reported the first death from coronavirus in the United States.
New York state confirmed its first positive coronavirus test, Governor Andrew Cuomo said on Sunday night.
He wrote on Twitter that a woman in her 30s contracted coronavirus during a recent trip to Iran and was in quarantine in her home.
He did not say where the woman lived, but the New York Times, citing unnamed state officials, said the woman was in New York City.
"The patient has respiratory symptoms, but is not in serious condition and has been in a controlled situation since arriving in New York," Cuomo said.
At the federal level, President Donald Trump's administration scrambled on Sunday to reassure Americans as the disease spreads and businesses cancel conferences and flights.
Administration officials tried to calm market fears that the coronavirus could cause a global recession, saying the public had overreacted and that stocks would bounce back because of the underlying strength of the US economy.
Washington state on Sunday confirmed two other cases at a long-term care facility where a resident and a worker also tested positive for coronavirus and 50 residents and staff were showing symptoms.
Over 70 cases have been reported in the United States, with most on the West Coast but new cases in the Chicago area and Rhode Island, aside from New York.
Trump said on Sunday that travelers to the United States from countries at high risk of coronavirus would be screened before boarding and on arrival, without specifying which countries.
The United States has 75,000 test kits for coronavirus and will expand that number "radically" in coming weeks, US Health and Human Services Secretary Alex Azar said.
Vice President Mike Pence said the government had contracted 3M Co to produce an extra 35 million respiratory masks a month. He urged Americans not to buy the masks, which he said were only needed by healthcare workers.
He also told Fox News that clinical trials of a coronavirus vaccine would start in six weeks but that a vaccine would likely not be available this season.
Pence, whom Trump appointed last week to run the White House's coronavirus response, said Americans should brace for more cases but that the "vast majority" of those who contracted the disease would recover.
The United States has imposed limits on travellers who have visited Iran and recommended against travel to hard-hit areas of Italy and South Korea.
Trump said on Saturday that the United States was also considering shutting the country's southern border with Mexico to control the spread of the virus, adding: "We hope we won't have to do that."
Mexico has reported four coronavirus cases.
Reuters
