Millions around the world yesterday braced for drastically curtailed New Year celebrations as record coronavirus cases fuelled by the Omicron variant saw the WHO warn a Covid "tsunami" threatens to overwhelm healthcare systems.

Coronavirus, first detected two years ago and declared a global pandemic in March 2020, has killed more than 5.4 million people, triggered economic crises and seen societies ricochet in and out of lockdowns.

The latest variant, Omicron, while tentatively considered to cause milder illness, has pushed infection levels to record levels in recent days in the United States, Britain, France and other European countries, forcing governments to reimpose restrictions.

The number of daily new Covid cases worldwide crossed one million for the first time, according to an AFP tally yesterday, with more than 7.3 million in the last seven days.

From Greece to Mexico, from Barcelona to Bali and across swathes of Europe, authorities have cancelled or curtailed public gatherings, either closing or imposed curfews on nightclubs.

In India, authorities yesterday started to impose stringent rules to prevent mass gatherings at new year's parties and public venues to combat a spike in Covid-19 infections, even as top leaders led large political rallies.

Night curfews have been imposed in all major cities and restaurants ordered to limit customers.

However, Prime Minister Narendra Modi and Home Minister Amit Shah presided over public rallies in northern states with footage from the events showing thousands of people gathered in open grounds to hear their speeches.

Last week an Indian court urged Modi's government to suspend political rallies and election campaigns in poll-bound states amid the rising number of Omicron cases.

In France, wearing masks outdoors will be compulsory while walking the streets of Paris from today for everyone over the age of 11. Nightclubs have been closed until well into January.

In Spain, public festivities have been cancelled across most regions and in the biggest cities except Madrid, where a stripped-down gathering is scheduled with the crowd limited to 7,000 people compared to 18,000 in 2019 before the pandemic swept Europe.

Yesterday, Britain's National Health Service announced that it would start opening temporary field hospitals to contain a possible overspill of inpatients in England, where the government stopped short of mandating curbs on New Year festivities.

"Given the high level of COVID-19 infections and increasing hospital admissions, the NHS is now on a war footing," National Medical Director Stephen Powis said.

Indonesia, which has reported more than 4.2 million confirmed cases, warned that foreign travellers may be deported from the resort island of Bali if they are caught violating Covid health rules during New Year.

"Get ready to be kicked out," Bali immigration office head Jamaruli Manihuruk told AFP. Bali has barred carnivals, fireworks and gatherings of more than 50 people over the Christmas and New Year period.

Mexico City has also cancelled its massive New Year's Eve celebrations as a preventative measure after a rise in Covid cases.

In Saudi Arabia, authorities reimposed social distancing measures at the Grand Mosque in the Muslim holy city of Mecca, after recording the highest number of infections in months.

"I am highly concerned that Omicron, being more transmissible, circulating at the same time as Delta, is leading to a tsunami of cases," said WHO chief Tedros Adhanom Ghebreyesus.

"This is and will continue to put immense pressure on exhausted health workers, and health systems on the brink of collapse."

Omicron has already started to overwhelm some hospitals in the United States, the hardest-hit country, where the seven-day average of new cases has hit 265,427, according to a Johns Hopkins University tracker.

Harvard epidemiologist and immunologist Michael Mina tweeted that the count was likely just the "tip of the iceberg" with the true number likely far higher because of a shortage of tests.

In China, residents in the city of Xi'an, where 13 million people are under lockdown, said they were struggling to find enough food, despite Beijing insisting that there were adequate supplies.