A homeless man pushes a shopping cart carrying his belongings in an empty street in Madrid. AFP

Coronavirus deaths surged past 100,000 in Europe as the world's top musicians joined forces for a virtual concert, hoping to spread cheer to billions stuck at home under lockdown.

A-listers including the Rolling Stones, Taylor Swift, Stevie Wonder and teen superstar Billie Eilish entertained fans with a six-hour online extravaganza celebrating healthcare workers.

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Over 2.25 million coronavirus cases registered worldwide

The event, set up by advocacy group Global Citizen with the World Health Organization, aimed to cultivate a sense of community during the pandemic, which has ravaged the global economy with nearly 2.3 million confirmed infections in total.

At least 157,000 people have been killed by COVID-19 with two-thirds of the deaths in Europe, according to an AFP tally, and nearly a quarter of fatalities in the United States, the worst-hit country.

A military personnel carries the coffin of a person deceased from coronavirus in Seriate, Italy, on Saturday. AFP

The highly contagious disease first emerged late last year in the city of Wuhan in central China. It was likely transmitted to humans at a market where exotic animals were slaughtered, Chinese scientists have said.

Conspiracy theories that the virus came from a maximum-security laboratory have been brought into the mainstream in recent days by US government officials.

An elderly COVID-19 patient is transferred to an ambulance from a Hospital in Barcelona, Spain. Felipe Dana/AP

Secretary of State Mike Pompeo said an investigation was underway into how the virus "got out into the world".

But the director of the virology institute in Wuhan rejected the claims on Saturday, saying it was "impossible" that the disease could have come from his lab.

Lockdown protests

The US has the highest caseload of any country, with more than 735,000 confirmed infections, and by Sunday had lost 38,910 people to the virus, according to a tally from Johns Hopkins University.

Progress was marked in some places, with New York state reporting the lowest number of deaths in weeks, which Governor Andrew Cuomo attributed largely to social distancing.

Staff prepare to load equipment into London Ambulance Service vehicles in the east car park at the ExCeL in London. AFP

But as Americans and others around the world chafe after weeks under stay-at-home orders, resentment is rising.

Anti-lockdown protests on Saturday drew hundreds of people at the capitols of states including Texas, Maryland, New Hampshire and Ohio. Many demonstrators waved American flags and some carried arms.

'My family is hungry'

Mounting evidence suggests that social distancing slowed the pandemic after more than half of humanity -- 4.5 billion people -- were confined to their homes.

Stay-at-home orders have been enforced in Italy and Spain, both still the hardest-hit countries in Europe, with death tolls over 20,000, followed by France, which has recorded more than 19,000 fatalities.

As governments around the world grapple with when and how to ease lockdowns, Spain on Saturday extended its nationwide shutdown to May 9.

Japan, Britain and Mexico have all expanded their movement restrictions.

Yet elsewhere, signs that the outbreak could be easing prompted Switzerland, Denmark and Finland to begin reopening shops and schools this week.

Germany has declared the virus "under control" after 3,400 deaths, and is beginning the delicate task of lifting some restrictions without triggering a secondary outbreak -- with some shops allowed to reopen Monday, and some children returning to school within weeks.