The impact of the coronavirus on everyday life deepened around the world, and it was detected for the first time in several more countries on Friday.
More schools and businesses closed to try to slow its spread, governments took other drastic steps, the global sporting calendar was left in tatters and people faced greater restrictions on where they could go.
"To unleash the full power of the federal government to this effort today, I am officially declaring a national emergency - two very big words," Trump said in remarks at the White House, adding that the US situation could worsen and "the next eight weeks are critical."
Trump had faced criticism from some experts for being slow and ineffective in his response to the crisis and playing down the threat.
The latest steps on Friday came two days after Trump announced travel restrictions blocking US entry for most people from continental Europe. While he exempted Britain at the time, on Friday he said that might change because UK infections have "gone up fairly precipitously."
Trump, who previously was pictured standing near a visiting Brazilian official who has tested positive for the virus, said he himself would be tested "fairly soon." But did not plan to isolate, noting he was suffering no symptoms.
Trump said the federal government was partnering with the private sector to accelerate production of test kits to make them more widely available to Americans in an effort to track the virus' spread.
But he said, "I don't take any responsibility at all" for the lack of needed testing capacity early on in the outbreak, instead blaming previous government policies. The US coronavirus death toll reached 46 on Friday after six more deaths were reported in Washington state.
EUROPE NOW EPICENTRE, SAYS WHO
The World Health Organisation called Europe the epicentre of a coronavirus pandemic after the number of cases in China, where it originated, slowed to a trickle.
The WHO called the death toll reaching 5000 globally "a tragic milestone."
The WHO's top emergency expert, Mike Ryan, said social distancing was a "tried and tested method" to slow the spread of a virus but "not a panacea" that would stop transmission.
"Blanket travel measures in their own right will do nothing to protect an individual state," Ryan said.
In Italy, which after China has been hardest hit by the respiratory illness, the death toll jumped by 250 to 1266 in the last 24 hours, authorities said. The total number of cases also rose to 17,660 from a previous 15,113, despite draconian measures to restrict the movement of people.
In the northern region of Lombardy, at the heart of Italy's coronavirus epidemic, authorities asked for even stricter steps.
Major Spanish regions shut shops, bars and restaurants and Easter parades were cancelled as Spain prepared to enter a 15-day state of emergency on Friday. The number of infections rose to 4231, up about 1000 cases from Thursday. About 120 people have died.
British cases of coronavirus rose 35% to 798 by Friday. There have been 10 deaths so far.
In Germany, the number of confirmed cases rose by 671 to reach 3062, the Robert Koch Institute for infectious diseases said, and five people had died after testing positive for the virus.
Meanwhile, more cultural landmarks were shuttered to try to stop the spread of the virus. In Paris, the Eiffel Tower, the Louvre museum and the Moulin Rouge cabaret closed their doors.
The Smithsonian museums in Washington were preparing to do so on Saturday and Broadway theaters in New York went dark.
The kissing of the Blarney Stone, one of Ireland's oldest tourist traditions, was suspended.
MARKETS HIT BY PANIC SELLING
The final global economic cost remains unknown, but travel bans have hammered airlines and travel companies, while financial markets have been hit by panic selling.
The three major US stock indexes rallied more than 9% on Friday, rebounding from Wall Street's biggest daily drop since 1987 after Trump declared the national emergency.
Despite a limited recovery on Friday, the main US stock indexes faced their biggest weekly declines since the 2008 financial crisis, and remain around 25% below the record highs achieved in mid-February.
Central banks worldwide acted to shore up money markets after cratering share prices drove a rush for cash, hitting many regional currencies and threatening a surge in short-term borrowing costs.
In China, which bore the brunt of the economic fallout from the coronavirus in the first few months of 2020, authorities late on Friday cut banks' reserve requirements for the second time this year.
Japan's central bank pledged to buy 200 billion yen ($NZ305 billion) of five- to 10-year Japanese government bonds and also inject an additional 1.5 trillion yen in two-week loans.
The European Union said it would establish a €37 billion ($67 million) investment initiative as part of a package of measures to cushion the bloc's economies from the impact of the coronavirus.
FIRST CASES IN AFRICA
In hard-hit Iran, security forces will empty the streets in cities across the country in a drive to fight the virus' spread, state television reported.
The virus continued its persistent march across the globe. Kenya, Ethiopia, Sudan and Guinea all confirmed their first cases, giving the disease a foothold in 18 countries on the African continent. Venezuela and Kazakhstan also confirmed their first cases.
In Washington, the State Department summoned the Chinese ambassador to protest comments by a Chinese foreign ministry spokesman saying the American military might have brought the coronavirus to the city of Wuhan, ground zero of the outbreak.
World leaders, sports stars and actors were among the tens of thousands of people hit by the virus.
Golf's crown jewel, The Masters, and England's top-flight soccer league joined the long list of elite sporting events to be canceLled or postponed.
Spain's La Liga, Italy's Serie A and the French Ligue 1 are all on hold and Germany's Bundesliga followed suit on Friday.
But sport's biggest showpiece, the Olympics, will proceed as planned, according to Tokyo organisers.
In Greece, home of the ancient Olympics, the nation's Olympic Committee canceled the remainder of the Olympic Torch relay through the country.
