WASHINGTON - President Donald Trump announced that the United States would suspend all travel from Europe from Friday (March 13) for 30 days to slow the spread of the coronavirus.

The announcement comes just hours after the World Health Organisation officially declared it a pandemic.

The travel restrictions would not apply to the United Kingdom, which Mr Trump said has 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 nation 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.

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 that many workers who could not afford to stay home when sick, would not.

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$69.8 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 American economy, said Mr Trump, who also called on Congress to provide immediate payroll tax relief.

He said the risk to the vast majority of Americans was low, but encouraged viewers at home to practise good hygiene even as more and more workplaces and event organisers adopt social distancing policies.

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

His administration also recommended that nursing homes suspend all medically unnecessary visits.

He also cancelled his upcoming events in Colorado and Nevada on Wednesday, the eve of a three-day trip that would have included a speech at the Republican Jewish Coalition national meeting in Las Vegas.

The cancellations were "out of an abundance of caution from the coronavirus outbreak", said his press secretary Stephanie Grisham in a statement.

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.

Earlier on Wednesday, National Institute of Allergy and Infectious Diseases head Anthony Fauci testified at a House hearing that the worst was yet to come.

"How much worse we'll get will depend on our ability to do two things: to contain the influx of people who are infected coming from the outside, and the ability to contain and mitigate within our own country," said Dr Fauci.

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.

"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," said Georgetown University global health law professor Lawrence Gostin on Twitter.

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."

Centre for Global Development's senior policy fellow Jeremy Konyndyk said: "Travel bans are like locking the doors after the killer has already entered the house. Economic support treats the symptoms not the disease."

Ms Amanda Glassman, executive vice-president of the Centre for Global Development, said: "We need a plan and guidance to slow the speed of Covid-19's spread, to test more widely and quickly, to scale up treatment, to ease the economic impact beyond tax breaks, and to assure that poor countries prepare to limit spread in the medium term."