President Donald Trump has announced that the United States will suspend all travel from Europe from today for 30 days to slow the spread of the coronavirus, a move that failed to calm Wall Street as stocks plunged the morning after the President's address.

The Dow Jones Industrial Average fell by 1,700 points just after trading opened yesterday, while the S&P 500 dropped 7 per cent, triggering a circuit breaker that halted all trading for 15 minutes to prevent markets from crashing.

The unilateral move was also condemned by the European Commission, which said it was not consulted before the ban was announced.

US Vice-President Mike Pence, however, defended the decision yesterday morning, saying the epicentre of the coronavirus pandemic had shifted from Asia to Europe.

Mr Trump said the restrictions would not apply to the United Kingdom, which he deemed as having taken more precautions than the European Union against the virus.

Americans who underwent the appropriate medical screenings would also be exempted, he said in a solemn address to the country from the Oval Office on Wednesday - only his second since taking office in 2017.

"We are at a critical time in the fight against the virus. We made a life-saving move with early action on China. Now, we must take the same action with Europe. We will not delay," he said.

The Department of Homeland Security later said in a statement that the restrictions would cover foreign nationals who had been in Europe in the past 14 days.

It would not apply to legal permanent residents, nor in general to immediate family members of American citizens.

The State Department, in a separate statement on Wednesday, advised all Americans to reconsider international travel.

In his address, Mr Trump also listed other measures taken by his administration to provide relief to individuals stricken by the virus, as well as to affected businesses.

Financial relief would be provided to workers who are ill, quarantined or caring for others, in an effort to encourage them to stay home if they are feeling sick.

Paid sick leave is not mandated under federal law in the US, and this gap in the country's social safety net came under fire in recent weeks as public health experts said many workers who could not afford to stay home when sick, would not do so.

The Small Business Administration would also provide capital and liquidity to firms affected by the coronavirus in the form of loans. Congress was being asked to increase funding for this programme by another US$50 billion (S$70 billion), Mr Trump said.

Tax payments for certain individuals and affected businesses would also be deferred, injecting more than US$200 billion of liquidity into the economy, he added.

He said the risk to the vast majority of Americans was low, but encouraged viewers at home to practise good hygiene.

He acknowledged elderly people with underlying health conditions faced the highest risk, and urged older Americans to avoid non-essential travel to crowded areas.

Wednesday night's address marked an increasingly serious tone taken by the Trump administration towards the pandemic, after the President downplayed it in its early days.

Public health experts said the temporary travel ban on Europe would have limited effectiveness, particularly as the virus was already being spread within communities in the US without individuals having travelled from abroad.

They also criticised the lack of attention paid to social distancing measures, and said the Trump administration should be doing more to boost testing and tracking the virus spread within the US.

Georgetown University global health law professor Lawrence Gostin said on Twitter: "Germs don't respect borders. Most of Europe has as much as, or more, cases than the US. Travel bans won't make the US safer."

Pandemic expert Laurie Garrett, a former senior fellow for global health at the Council for Foreign Relations, tweeted: "From the beginning of the Covid-19 epidemic, our government has pulled up (the) travel drawbridge to protect the US castle. But the virus is here, the strategy failed. We need all-out public health mobilisation."