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.