After coming under criticism that they were mismanaging the response, both London and Washington announced massive economic stimulus packages.
President Donald Trump said the White House was discussing a "substantial" spending bill with Congress that would include immediate cash payments to US citizens in a bid to pull the economy from growing fears of recession.
Officials did not give hard numbers but The Washington Post reported the amount could reach $850 billion, with a chunk destined for airlines fearing ruin.
"We're going big and that's the way it'll be," Trump told reporters.
British Finance Minister Rishi Sunak unveiled an "unprecedented package" of government-backed loans worth £330 billion ($400 billion) for businesses struggling in the sudden economic paralysis caused by mass self-quarantine.
France also pledged a 45 billion euro ($50 billion) aid package.
German Chancellor Angela Merkel confirmed a 30-day "entry ban" into the European Union, saying that Germany would move to "implement it immediately."
European countries were already in near total internal lockdown as the World Health Organization urged the "boldest actions" on the continent, the pandemic's latest epicentre.
In the United States, restrictions continued to build, with Maryland becoming the latest state to delay presidential election primaries and New York City considering curfews. Australia ordered citizens not to travel abroad.
The draconian measures, never before seen in peacetime, upended society worldwide and roiled financial markets on fears of a global recession.
Usually joyful -- and alcohol-fueled -- Saint Patrick's Day celebrations were canceled in Dublin, New York and Boston.
The sports world has been hammered too, with the Euro 2020 the latest tournament to be postponed and major doubts over the fate of the Tokyo Summer Olympics.
The outbreak, which first emerged in China late last year, has quickly marched across the globe, infecting more than 190,000 people and killing 7,900.
Asian hotspots China and South Korea have seen new infections and deaths level out in recent weeks -- China reported just one new domestic case on Tuesday -- but numbers are ballooning across Europe.
Africa, with its fragile healthcare systems, has also recorded more than 400 cases, and Latin America has more than 1,100, with the continent's most populated country Brazil confirming its first death Tuesday.
'Invisible enemy'
Trump, who for weeks has been accused of playing down the crisis, appeared determined to take control of his messaging, declaring he would do everything to fight an "invisible enemy."
"We have to win this war," he said in a White House where staff and journalists now have to undergo regular temperature checks.
Battered US stocks -- something Trump sees as a key metric of his success ahead of November presidential elections -- closed 5.2 percent higher after the economic stimulus announcement.
On Monday, Trump acknowledged that the economy, which is arguably his strongest card for winning a second term, might be sliding into recession.
In France, President Emmanuel Macron also likened the outbreak to a war and ordered almost the entire population to stay at home.
People are only permitted to leave their houses on a limited basis -- to buy food or for health reasons, for example.
About 100,000 police and gendarmes will be on the streets to enforce the measures, which are in place for at least two weeks.
Showing some of the public spirit under pressure also witnessed in Italy and Spain, thousands of Parisians took to their balconies at 8:00 pm to bang pots, blow trumpets and clap in a show of support for health workers.
Britain stepped up its own measures following scientific advice that infections and deaths would spiral without drastic action.
Citizens were told to avoid all non-essential overseas travel and large social gatherings, with more stringent restrictions expected in the coming days.
Germany has banned gatherings in churches, mosques and synagogues and said playgrounds and non-essential shops would close, too.
In Ireland, Anthony Whyte, 49, looked out onto the cobbled streets of Dublin from a bar and likened the scene to "a ghost town."
"It's like armageddon," he said.
Markets buoyed
Following a hammering in recent days, US and European markets bounced back.
Despite the wild swings, Treasury Secretary Steven Mnuchin ruled out a temporary closure of stock markets, saying "Americans need to know they have access to their money."
The strong expressions of support from Western economic chiefs came a day after the G7 leaders vowed in a conference call to "do whatever it takes" to prevent the health crisis turning into a financial meltdown.
However, every sector from tourism to food to aviation is affected, as the global economy effectively goes into shutdown.
German giant Volkswagen on Tuesday joined other European carmakers in closing down plants, swiftly followed by Mercedes-Benz parent company Daimler which said most European operations would be suspended.
Major world airlines have axed almost all flights temporarily, triggering pleas to help carriers survive.
Italy announced plans to renationalize national carrier Alitalia, and France said it was ready to nationalize large companies if necessary.
- Euro 2020 postponed -
The European Championship was postponed until next year and the Tokyo Olympics -- due to start in July -- hang in the balance, though Japanese officials insist the event will go ahead.
The French Open was also postponed Tuesday, now scheduled to start in September instead of May.
Drugmakers are scrambling for breakthrough, though it could still take more than a year before a safe vaccine is ready to market.
US health officials said the first human trial to evaluate a possible vaccine had begun.
French pharmaceutical giant Sanofi and American drugmaker Regeneron said they had started clinical trials for Kevzara, a drug currently used to treat rheumatoid arthritis and which they hope will reduce lung inflammation in severe cases of coronavirus illness.
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