America ramped up its response to the coronavirus pandemic on Sunday as the Federal Reserve took sweeping action to stem the economic fallout, Puerto Rico declared a curfew, New York closed schools, and California locked down its bars and restaurants.

The fast-spreading pandemic has claimed more than 60 lives in the United States, disrupting every walk of life as Americans -- watching Europe plunge into lockdown as panic-buying spreads at home -- brace for what is yet to come.

Faced with an economic shutdown, the Fed announced a raft of drastic emergency measures to shore up confidence and keep the financial sector running, including slashing the key interest rate to 0-0.25 percent.

President Donald Trump, addressing a now-daily briefing of the White House task force on the crisis, praised the "phenomenal" action by the Fed, and sought a reassuring tone even as he pleaded with Americans to stop stripping store shelves bare.

"Relax. We're doing great. It all will pass," the president said.

But task force member Anthony Fauci, the country's leading expert on infectious diseases, was blunt in telling Americans to prepare for a worsening situation, saying it was vital the country made the right choices in coming weeks.

"The worst is ahead for us," said Fauci. "We have a very, very critical point now."

Underscoring the sense of urgency, New York's Mayor Bill de Blasio announced the closure of public schools in America's biggest city, bowing to pressure after strongly resisting the move.

Schools, museums, sports arenas and entertainment venues have already closed in many US states, but St Patrick's Day celebrations still filled bars and restaurants over the weekend despite pleas to limit socializing, prompting calls for more aggressive action.

Reinforcing the message, the Centers for Disease Control and Prevention issued new nationwide guidance Sunday recommending that organizers cancel or postpone any in-person events gathering 50 people or more -- with the exception of day-to-day activities in education or business.

- 'Not a joke' -

In the strongest measure yet taken on American soil, the US territory of Puerto Rico, the governor ordered a 9:00 pm to 5:00 am curfew with immediate effect -- along with the closure of malls, movie theaters, concert venues, gyms and bars.

And in the largest state of California, Governor Gavin Newsom called for bars and nightclubs to close, and asked all people over the age of 65 to self-isolate at home.

The governor of Illinois announced that all bars and restaurants in the state would close until March 30 -- noting that crowds continued to pack Chicago's bars on Saturday night

"The time for persuasion and public appeals is over. This is not a joke. No one is immune to this," Governor JB Pritzker told a news conference.

- Airport chaos -

Chaotic scenes erupted at Chicago's O'Hare International Airport overnight as Americans returning from coronavirus-hit countries overwhelmed authorities attempting to process the surge.

Similar conditions were reported at New York's John F. Kennedy Airport and in Dallas.

US airports have been hit with a flood of Americans since restrictions on travel from Europe ordered by Trump took effect at midnight Friday. The ban will extends Tuesday to Britain and Ireland.

Frustrated passengers complained of hours-long lines, crowded and unsanitary conditions in the system for screening people for symptoms of the virus.

Pritzker was biting in his criticism of the administration's handling of the crisis, firing off angry tweets at Trump and Vice President Mike Pence.

He said Pence had promised an immediate doubling of screening capacity and by mid-afternoon Sunday, passengers arriving at O'Hare reported a more hassle-free entry.

- Testing to ramp up -

The airport bottlenecks were the latest evidence of continuing turbulence in the administration's response to a pandemic that started in China in December and has since spread worldwide.

In the United States, 62 people have died from the virus and more than 3,200 have been infected, according to a running tally kept by Johns Hopkins University.

But the pandemic has outpaced the government's capacity to measure its true scope through wide-scale testing.

Addressing Sunday's briefing, Vice President Mike Pence said free testing was now available in all 50 states and that "more than 2,000 labs" were now equipped to process tests "much more rapidly, at a much higher volume."

Task force coordinator Deborah Birx warned, however, that people should be prepared to see case numbers surge as testing capacity ramps up.

"We are going to see a spike as more and more people have access," she said.

Trump, who had played down the risks of infection early on, has tested negative for the virus, days after potentially being exposed to it during a visit by Brazil's President Jair Bolsonaro.

The White House is now performing systematic temperature checks on anyone in close contact with the president.