A Covid variant-driven "tsunami" threatens to overwhelm healthcare systems, the WHO said Wednesday as AFP data showed cases have surged across the world in the past week to levels never seen before.

Highly transmissible Omicron propelled the United States, France and Denmark to fresh records on Wednesday, with AFP's tally of 6.55 million infections reported globally for seven days through Tuesday showing the unprecedented spread.

Studies suggest Omicron causes a milder Covid-19 with a reduced risk of being admitted to hospital
Studies suggest Omicron causes a milder Covid-19 with a reduced risk of being admitted to hospital AFP / Hollie Adams

They were the highest figures since the World Health Organization declared a pandemic in March 2020, underscoring the blistering pace of Omicron transmission, with tens of millions of people facing a second consecutive year of restrictions dampening New Year's Eve celebrations.

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

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

The surge, currently worst in Europe, is forcing governments to walk a tightrope between imposing restrictions designed to stop hospitals from becoming overwhelmed and the need to keep economies and societies open two years after the virus first emerged in late 2019.

The United States, where Omicron is already overwhelming hospitals, recorded its highest-ever seven-day average of new cases at 265,427, according to a tracker maintained by Johns Hopkins University.

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

One week of new Covid-19 cases
One week of new Covid-19 cases AFP / John SAEKI

But the country also appears to be experiencing a decoupling between infections and severe outcomes compared to previous waves, officials noted, as evidence accumulates of milder outcomes under the new variant.

France on Wednesday registered a new daily record of more than 200,000 cases -- more than double the number recorded on Christmas Day -- and extended into January the closure of nightclubs.

Denmark, which currently has the world's highest rate of infection per person, recorded a fresh record of 23,228 new infections, which authorities attributed in part to the large numbers of tests carried out after Christmas celebrations.

The WHO says further data is needed to understand Omicron's severity
The WHO says further data is needed to understand Omicron's severity AFP / Sajjad HUSSAIN

Portugal also saw a record with nearly 27,000 cases reported in 24 hours, while Lebanon had 3,150 new infections -- its highest daily tally since vaccines rolled out earlier this year.

Spread of the coronavirus
Spread of the coronavirus AFP / Simon MALFATTO

Studies suggest Omicron, now the dominant strain in some countries, carries a reduced risk of being admitted to hospital, but the World Health Organization still urged caution.

More than 5.4 million people around the world have died from Covid-19, but over the last week the number of deaths averaged 6,450 a day, the AFP tally said, the lowest since October 2020.

In Europe, where more than 3.5 million cases have been recorded in the last seven days, Greece banned music in bars and restaurants until January 16, including on New Year's Eve.

French lawmakers were to start debating a new law that will only allow those vaccinated to enter restaurants, cinemas, museums and other public venues -- no longer those showing proof of a negative Covid test.

Germany has put restrictions on sports competitions and shut nightclubs, limiting private gatherings to 10 vaccinated people -- or two households where any unvaccinated people are present.

British Prime Minister Boris Johnson said around 90 percent of coronavirus patients in intensive care units had not had a booster jab, defending his decision not to clamp down on festivities.

The high take-up of boosters in England "is allowing us to go ahead with New Year in the cautious way that we are," he said despite new closures in Northern Ireland, Scotland and Wales.

In Asia, Vietnam -- an export-reliant economy long seen as a success story -- reported economic growth for 2021 at a 30-year low of just 2.58 percent, as the pandemic takes its toll.

Armed police in Jingxi in southern China, near the border with Vietnam, paraded four alleged violators of Covid rules through the streets, state media reported, a practice that was banned but which has resurfaced in the struggle to enforce a zero-Covid policy.

Mexico City's mayor on Tuesday cancelled the capital's massive New Year's Eve celebrations as a preventative measure after a rise in Covid-19 cases.

In Ukraine, three people died after a candle lit by a hospital employee in memory of a patient who died of the virus, started a fire in an intensive care unit in the western town of Kosiv.

"Ignorance of the elementary laws of physics and disregard for safety rules have led to irreparable losses," the emergencies services said, describing the incident as a "terrible mistake".