The United States neared six million coronavirus cases on Sunday, nearly a quarter of the planet's total, as nations around the world battle to contain the raging pandemic.

Global coronavirus infections soared past 25 million, as countries tightened restrictions to halt the health crisis that has upended life for most of humanity.

A million additional cases have been detected globally roughly every four days since mid-July, according to an AFP tally, with India on Sunday setting the record for the highest single-day rise in cases with 78,761.

The world's hardest hit country, the United States, had recorded 5.99 million cases of infection as of 0030 GMT Monday, according to Johns Hopkins University's tracker. And the death toll is just over 183,000.

The US hit five million cases three weeks ago, just 17 days after reaching four million, the tracker said.

The virus has hobbled the US economy, the world's largest, and cast a shadow over President Donald Trump's once-promising reelection prospects.

As Trump faces enormous pressure to curb the contagion, the head of the US Food and Drug Administration, Stephen Hahn, raised the possibility that a still-elusive vaccine might be given emergency approval before the end of trials designed to ensure its safety and effectiveness.

The virus has proven a tenacious foe even in nations such as New Zealand and South Korea, which had previously brought their outbreaks largely under control but are now battling new clusters of infections.

On the other side of the world, Latin America — the worst-hit region — is still struggling with its first wave, with Covid-19 deaths in Brazil crossing 120,000, second only to the United States.

Nearly 855,000 people have died of Covid-19 globally, and with no vaccine or effective treatment available yet, governments have been forced to resort to some form of social distancing and lockdowns to stop the spread of the virus.

Masks will become mandatory from Monday on public transport and flights in New Zealand, which went more than 100 days without local transmission before the current cluster emerged.

And tightened virus curbs kicked in on Sunday in South Korea, which is also battling fresh clusters — including in the greater Seoul region, home to half the country’s population.

In Iraq, thousands of Shiite pilgrims wearing gloves and masks flooded the holy city of Karbala to mark Ashura, in one of the largest Muslim gatherings since the pandemic began.

Typically, millions of Shiites from around the world flock to the shrine, but this year’s commemoration was subdued with employees spraying disinfectant mist, checking temperatures and enforcing social distancing.

"It stands out because there are so few people,” said Fadel Hakim, a blue medical mask cupping his chin.

‘Anti-corona’ rallies in Europe 

Despite all the grim numbers, there has been steady opposition to lockdowns and social distancing measures in many parts of the world, often because of their crushing economic cost.

But resistance has also come from the extreme right and left of the political spectrum, as well as conspiracy theorists and anti-vaccine campaigners.

In Berlin on Saturday, thousands gathered to march against coronavirus restrictions — but police later stopped the rally because many participants were not respecting social distancing measures.

Protesters waved German flags and shouted slogans against Chancellor Angela Merkel often used by the far-right Alternative for Germany  Party.

Similar protests were held in London and Zurich, where some carried signs supporting the far-right QAnon movement, which promotes bizarre theories about Satan-worshipping cabals and "deep state” plots — without any credible evidence.

The pandemic has upended economies and societies around the world, and halted most large gatherings — from sport and music to religion and politics.

In Spain, football superstar Lionel Messi missed a virus test at Barcelona’s training ground, club sources confirmed, raising the possibility he will boycott pre-season to force a transfer from the Spanish club.

Without a coronavirus test, Messi will be unable to join team-mates for new coach Ronald Koeman’s first training session on Monday.

The world’s top sport, culture and music events are struggling with the challenge of hosting spectators while reducing the risk of virus transmission.

The US Open Tennis tournament was also hit, announcing an unidentified player had been withdrawn after testing positive.