The White House has acknowledged the nation does not have enough coronavirus test kits as cases of the disease ticked upwards on both US coasts.
Vice-President Mike Pence said the Trump administration would not be able to meet its objective of delivering one million testing kits this week.
Congress meanwhile moved with unusual speed to approve a bumper emergency aid package to combat the outbreak.
Globally, authorities have confirmed more than 92,000 cases of the virus.
The vast majority - 80,552 - are in China, where the virus originated. To date, 3,042 people have died in the country.
The US death toll from the coronavirus climbed to 12 on Thursday, with all but one of the victims in the north-western US state of Washington.
There are now more than 200 cases of Covid-19 in 20 states.
A cruise ship, the Grand Princess, remains off the California coast while passengers are tested for the virus.
What do I need to know about the coronavirus?
Where is it spreading?
In Washington, officials in the Seattle area announced 20 new cases of the virus, bringing the total in that state to 70, according to its health department.
Nine of the US dead so far were from the same nursing home in suburban Seattle, which is now being investigated by authorities to see if it followed infection-prevention guidelines.
Some major Seattle-area businesses, including Microsoft and Amazon, have shut down some operations or urged employees to work from home.
New York saw its caseload double overnight to 22, all of them in or near the city. The city's mayor called on the federal government to send more test kits urgently.
About 200 people have been quarantined in the US state of Rhode Island because of their links to a school trip to Italy that has resulted in three cases of the coronavirus.
San Francisco reported its first two cases of the coronavirus on Thursday. And the US state of Maryland confirmed its first three cases, in the Washington DC suburbs.
Where are the testing kits?
At a press briefing on Monday, Food and Drug Administration Commissioner Stephan Hahn said close to a million tests would be ready by the end of this week.
But Vice-President Pence - who is co-ordinating the US response to the outbreak - conceded on Thursday that that target would not be met.
"We don't have enough tests today to meet what we anticipate will be the demand going forward," Mr Pence said during a visit to a factory in Minnesota.
Speaking in Washington state in the evening, Mr Pence said: "We still have a ways to go to ensure that tests are available."
But he said that by the end of next week the US government's diagnostic supplier would distribute kits across the country that would enable 1.2 million Americans to be tested for coronavirus.
President Donald Trump says the US has had relatively few confirmed cases of the virus because of his administration's decision to prohibit US entry to foreign nationals who have visited China - the epicentre of the outbreak - and Iran during the previous 14 days.
But health experts fear the virus may be spreading undetected in US communities because of a lack of testing kits.
The president is expected to sign an $8.3bn (£6.4bn) funding bill passed 96-1 by the US Senate on Thursday. It is intended to help state and local governments combat the coronavirus.
What's the latest on the Grand Princess cruise ship?
Officials ordered a cruise ship with about 3,500 people on board - including 142 Britons - to lie at anchor off the California coast until passengers and crew can be tested, after a previous voyager on the vessel died of the virus.
On Thursday, a Coast Guard helicopter lowered test kits on to the 951ft (290m) Grand Princess vessel by rope.
Princess Cruise Lines said fewer than 100 people aboard had been identified for testing. Results are expected by Friday.
"The ship will not come on shore until we appropriately assess the passengers," California Governor Gavin Newsom said.
A man who sailed on the Grand Princess last month died of the coronavirus on Wednesday. The 71-year-old from the Sacramento area had underlying health conditions, said officials.
Two other passengers from that voyage are in hospital with the virus in northern California, officials said.
Two helicopters approaching the #GrandPrincess with #coronavirus test kits. Again, my parents are on board (as well as many other parents and siblings and children). Please pray for them. @PrincessCruises @GavinNewsom @KTVU #COVID19 pic.twitter.com/XwlqTdV1uJ— Keane Li (@keaneli) March 5, 2020
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How is Wall Street reacting?
Concerns about the economic impact of the outbreak slammed Wall Street shares again on Thursday, sending the three main US stock indexes down more than 3%.
Travel companies were again some of the hardest hit, with shares in Royal Caribbean Cruises sinking more than 16% and Carnival Corp dropping 14%.
Airlines also suffered double-digit declines, after the International Air Transport Association warned the industry could lose as much as $113bn this year.
What is happening elsewhere?
- In Iran, at least 107 people have died from the virus and authorities have limited travel between major cities to curb the outbreak. Schools are also closed in the country until April
- Iraq has announced its first two confirmed deaths, one of them in the capital Baghdad
- Israel and the Palestinian Authority have put the city of Bethlehem under quarantine after seven people were diagnosed with the coronavirus there
- Canada has announced nine new cases, eight of them in its westernmost province, British Columbia - this brings the national total to 45
- The UK recorded its first death on Thursday - an older patient with underlying health conditions. The number of UK people diagnosed with the virus has reached 116, a rise of more than 30 since Wednesday
- Italy reported 41 new deaths on Thursday, the highest single-day toll so far, bringing its total to 148. The country has closed all schools and universities for at least 10 days
- The Paris Marathon has been postponed to a later date, French media report. About 65,000 runners were registered to take part, Le Parisien said
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