After White House officials took the unprecedented step of checking the temperatures of journalists entering the briefing room, the president told reporters he took a test for the virus on Friday night. On Saturday evening, his physician, Sean Conley, said the results were negative.

The US president met with a Brazilian delegation last week, at least one member of which has since tested positive.

Trump said Americans should reconsider non-essential travel, and that his administration was also considering domestic travel restrictions.

Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the country has recorded 2,226 cases of the new coronavirus but has not yet reached the peak of the outbreak.

"This will get worse before it gets better," Surgeon General Jerome Adams said at the briefing. But, he added, "99 per cent of people will recover and people need to know that".

Critics have accused Trump of focusing too much on markets, which on Friday saw the three major Wall Street indexes gain more than 9 per cent after having had their worst day since 1987 on Thursday.

All three indexes were nevertheless down at least 8 per cent for the week and about 20 per cent below mid-February record highs.

At the briefing, Trump told reporters he was "honored to see that the stock market set a record in a short period of time over a 45-minute period." He called it an "all-time record" that he hoped would be repeated daily.

Vice President Mike Pence, who is running the White House's response to the outbreak, said the administration was extending to Britain and Ireland travel restrictions that were first imposed on China and expanded this week to continental Europe.

Trump spoke to British Prime Minister Boris Johnson on Saturday about the new restrictions, the White House said.

US airlines, which have already been battered by the restrictions and a steep drop in demand, said on Saturday that they were preparing more flight cuts. Pence said the new restrictions will take effect at midnight on Monday.

Chad Wolf, acting secretary of the U.S. Department of Homeland Security, said Trump decided to add Britain to the travel ban because of the rising number of coronavirus cases there. Health authorities in England announced on Saturday a further 10 deaths caused by COVID-19, almost doubling the number of fatalities in Britain since Friday.

A senior DHS official, who spoke on condition of anonymity, said Britain and Ireland were added because the United States was not able to effectively determine whether travellers from those countries were trying to sidestep the European travel ban.

US citizens and legal residents will still be able to return home and will be funnelled through certain airports, Pence said.

The vice president also told reporters that visits to nursing homes were being suspended to protect the most vulnerable.

Nationwide, at least 58 people have died.

The pandemic has forced public schools, sports events and cultural and entertainment venues to close across the United States.

American shoppers picked grocery store shelves clean of products ranging from disinfectants and toilet paper to rice and milk, causing retailers to race to restock their stores. In response to the run on certain items, major retailers have imposed some purchase limits.

Early on Saturday, the US House of Representatives passed a coronavirus aid package that would provide free testing and paid sick leave, in a bid to limit the economic damage from the outbreak.

Economists say the impact of the outbreak on businesses could tip the US economy into recession.

Australian Associated Press