The World Health Organization has warned of a “tsunami of cases” of Covid-19 around the world as countries including France and the US reported record-breaking infection tallies.

Speaking to reporters on Wednesday, Tedros Adhanom Ghebreyesus, the WHO’s director-general, used the disaster analogy to describe how the higher transmissibility of the Omicron coronavirus variant was compounding the circulation of the Delta strain.

“This is and will continue to put immense pressure on exhausted health workers and health systems on the brink of collapse and again disrupting lives and livelihoods,” Tedros told reporters as the health body marked the two-year anniversary of the emergence of the pandemic.

WHO officials have noted that preliminary studies from several countries showed the Omicron variant driving the surge produced less severe outcomes than previous strains, but Tedros said the world’s healthcare systems still faced a stiff test.

“There is this narrative going on which is ‘it’s milder or less severe’,” Tedros said. “But we’re undermining the other side, at the same time it could be dangerous, because the high transmissibility could increase hospitalisations and deaths.”

His comments came after the US seven-day rolling average of cases breached 265,000 on Tuesday, its highest daily tally since the start of the pandemic, according to data from Johns Hopkins University.

Speaking to reporters on Wednesday, Rochelle Walensky, director of the Centers for Disease Control and Prevention, said: “In a few short weeks, Omicron has rapidly increased across the country and we expect will continue to circulate in the coming weeks.”

In France, health minister Olivier Véran said the country was facing a two-pronged “tidal wave” with Omicron and Delta.

France registered 208,000 positive cases on Wednesday, Véran said, a one-day record since the start of the pandemic. Testing has increased, he said, but the rate at which cases were spreading was unprecedented.

Meanwhile, Germany recorded 13,129 cases of infection with the Omicron variant on Wednesday, a 26 per cent increase on the previous day, according to official figures released by the Robert Koch Institute, the country’s main public health agency.

Karl Lauterbach, health minister, said the situation was much worse than the official data suggested, estimating that the actual incidence of coronavirus in Germany was twice or three times higher.

He called the “clear increase” in cases of Omicron “concerning”, and appealed to people to celebrate New Year’s Eve in a way that did not lead to new chains of infection. “Please celebrate in small groups,” Lauterbach said.

In the US, Anthony Fauci, Joe Biden’s chief medical adviser, acknowledged increasingly strong evidence of “lesser severity” of Omicron, either because of greater immunity to the virus or milder intrinsic virulence, but said it was no reason for complacency.

He told CNBC on Wednesday that he expected the Omicron wave in the US to peak “probably by the end of January”.

Still, US health officials at the CDC have issued new guidelines shortening the quarantine timeline for people infected with the coronavirus to five days if they show no symptoms.

“We know that after five days people are much less likely to transmit the virus,” Walensky said.

At the WHO, Tedros lamented the slow progress in distributing vaccinations around the world.

More than 90 countries globally have missed the target of vaccinating 40 per cent of their populations by year’s end because of a combination of limited supply and vaccines arriving close to the expiration date or without critical components such as syringes, Tedros said.

“Forty per cent was do-able,” he added, warning aggressive booster programmes in richer countries could again cause shortages in poorer countries despite increasing supply early next year. “It’s not only a moral shame, it cost lives and provided the virus with opportunities to circulate unchecked and mutate.”

A Financial Times analysis published this month showed Covid boosters in rich countries outnumbered all vaccines among poor nations. Scientists have long warned that uneven access to vaccines, coupled with high transmission, could lead to more troublesome variants.

The WHO is calling for all countries to vaccinate at least 70 per cent of their populations by mid-2022.