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 - more than 80,000 - are in China, where the virus originated. Worldwide, more than 3,000 people have died.
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.
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.