President Donald Trump partially blocked immigration to the United States "to protect American workers" from the economic shock of the coronavirus, as the United Nations warned the world was facing "a humanitarian catastrophe".

Hundreds of protesters take part in a "Reopen Pennsylvania" demonstration against coronavirus-related lockdowns in the state capital Harrisburg Hundreds of protesters take part in a "Reopen Pennsylvania" demonstration against coronavirus-related lockdowns in the state capital Harrisburg Photo: AFP / Nicholas Kamm

The UN alarm bell came as nations scrambled to fight the virus -- which has killed 177,000 people and infected more than 2.5 million -- as well as desperately seek ways to limit the vast damage inflicted on the global economy.

With more than half of humanity under some form of lockdown, businesses shuttered and millions of jobs lost, the world is facing its worst economic downturn since the Great Depression, and the UN's World Food Programme (WFP) said it would hit the least privileged the hardest.

US President Donald Trump says the country is heading in the right direction in terms of the evolution of the coronavirus crisis US President Donald Trump says the country is heading in the right direction in terms of the evolution of the coronavirus crisis Photo: AFP / MANDEL NGAN

"I want to stress that we are not only facing a global health pandemic, but also a global humanitarian catastrophe," WFP executive director David Beasley told the UN Security Council on Tuesday.

Germany has allowed some small shops to open Germany has allowed some small shops to open Photo: AFP / THOMAS KIENZLE

"Millions of civilians living in conflict-scarred nations... face being pushed to the brink of starvation."

The WFP warned the number of people suffering from acute hunger was projected to nearly double to 265 million this year.

Anti-lockdown demonstrations in the US over the weekend drew hundreds of people in states including Colorado, Texas, Maryland, New Hampshire and Ohio Anti-lockdown demonstrations in the US over the weekend drew hundreds of people in states including Colorado, Texas, Maryland, New Hampshire and Ohio Photo: AFP / Jason Connolly

In the United States, where some 22 million people have lost their jobs, Trump said he would stop the issuing of green cards for 60 days, but exempt temporary workers such as seasonal farm laborers.

World map showing official number of coronavirus deaths per country, as of April 20 at 1900 GMT World map showing official number of coronavirus deaths per country, as of April 20 at 1900 GMT Photo: AFP / Simon MALFATTO

"In order to protect American workers, I will be issuing a temporary suspension of immigration into the United States," he said.

"It will help put unemployed Americans first in line for jobs as America reopens.

Nurseries in Norway reopened Monday Nurseries in Norway reopened Monday Photo: AFP / Pierre-Henry DESHAYES

"It would be wrong and unjust for Americans to be replaced with immigrant labor flown in from abroad."

Health care workers in Madrid wearing protective suits examine a man who has fallen ill at home -- Spain is one of the countries worst hit by the coronavirus crisis Health care workers in Madrid wearing protective suits examine a man who has fallen ill at home -- Spain is one of the countries worst hit by the coronavirus crisis Photo: AFP / OSCAR DEL POZO

The US -- with nearly 45,000 deaths and more than 800,000 coronavirus infections -- is the hardest-hit country, and healthcare infrastructure in major hotspots such as New York City has struggled to cope.

The huge patient numbers are also taking a toll on the mental health of doctors and nurses.

Number of people in serious food insecurity, according to the Food and Agriculture Organisation. Number of people in serious food insecurity, according to the Food and Agriculture Organisation. Photo: AFP / Robin BJALON

"The same thing every day... is draining," said Heather Isola, a physician assistant.

People in need sit maintaining social distancing after collecting free food items outside the Badshahi mosque in Lahore, Pakistan People in need sit maintaining social distancing after collecting free food items outside the Badshahi mosque in Lahore, Pakistan Photo: AFP / ARIF ALI

"What is it going to do to us? The anxieties, the PTSD, the experience of death and dying. Most people haven't seen death and dying like this."

The director of the US Centers for Disease Control, meanwhile, called on Americans to prepare for a second wave of infections.

Cementery workers wearing protective gear bury an unclaimed COVID-19 victim, at the Municipal cementery No. 13 in Tijuana, Baja California state, Mexico Cementery workers wearing protective gear bury an unclaimed COVID-19 victim, at the Municipal cementery No. 13 in Tijuana, Baja California state, Mexico Photo: AFP / Guillermo Arias

"There's a possibility that the assault of the virus on our nation next winter will actually be even more difficult than the one we just went through," Robert Redfield told the Washington Post.

Nurses employed at Providence Saint John's Hospital and their supporters demand better protective equipment in Santa Monica, California Nurses employed at Providence Saint John's Hospital and their supporters demand better protective equipment in Santa Monica, California Photo: AFP / Frederic J. BROWN

Nurses hold a protest in front of the White House in Washington, DC, to call attention to the tens of thousands of health care workers nationwide who have become infected with COVID-19 due to lack of personal protective equipment. Nurses hold a protest in front of the White House in Washington, DC, to call attention to the tens of thousands of health care workers nationwide who have become infected with COVID-19 due to lack of personal protective equipment. Photo: AFPTV / Gilles CLARENNE

Some countries in Europe have started easing lockdowns as the spread of the virus is slowly brought under control, but the cancellation of more well-known events served as a reminder that the pandemic is far from over.

In Germany, where small shops have been allowed to reopen, authorities canceled this year's Oktoberfest, the beloved beer-swilling festival in southern Bavaria, for the first time since World War II.

The German government's restrictions on large gatherings also mean the Berlin Marathon will not go ahead as planned this year in September, organizers said.

Spain, which is set to allow children some movement in a week, said it was scrapping the annual bull-running festival in Pamplona.

The pandemic has ripped apart the global sports calendar -- most notably forcing the postponement of the Tokyo Olympics to next year.

German football authorities are expected to announce plans on Thursday for its top-level league to restart matches in empty stadiums on May 9.

But the Dutch football federation said it intended to end its season because of the extension of a ban on large gatherings.

Across the Atlantic, the NFL draft -- a three-day annual glitzy marketplace to choose the top collegiate talent -- will be held online from Thursday, with teams making their picks from remote locations across the United States.

Global markets remain under intense pressure because of the pandemic.

With billions locked down, economies halted and travel extremely limited, a dramatic drop in the demand for oil has sent prices crashing in recent weeks.

Major cuts promised by the world's top oil producers have failed to stabilize the market, and the rout continued on Wednesday.

Extraordinary stimulus measures worth trillions of dollars gave some boost to stock markets, but have failed to lift the overall mood on trading floors.

Like with the food crisis warning from the WFP, the biggest impact of the loss of jobs and the overall economic downturn is being felt by the most disadvantaged.

They include the millions of migrant workers from South Asia and elsewhere that toil in the Middle East to send money back home to their families.

"Nobody comes anymore, nobody touches, nobody says goodbye," said Ishwar Kumar, manager of a Hindu cremation ground in Dubai.

Before the pandemic, people would come "to grieve and bring flowers. Now they die alone".