The Omicron coronavirus variant has now spread to 89 countries and the number of cases is doubling in 1.5 to 3 days in areas with community transmission, according to a WHO statement on Saturday.

Omicron is spreading rapidly, but it is unclear if this is due to the virus's ability to evade immunity, its inherent increased transmissibility or a combination of both, the UN agency said.

More data are still needed to understand the severity profile and how severity is impacted by vaccination and pre-existing immunity, WHO further stated.

The World Health Organization has warned that the Omicron variant of COVID-19 is spreading at an unprecedented rate and urged countries to act

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Earlier this week, WHO chief Tedros Adhanom Ghebreyesus urged countries to act swiftly to rein in transmission and protect their health systems and warned against complacency.

WHO expert Bruce Aylward emphasised against "jumping to a conclusion that this is a mild disease".

"We could be setting ourselves up for a very dangerous situation," he added.

Omicron, first identified by South Africa and reported to the WHO in late November, has over 30 spike proteins which has raised fears that it has the potential to break through vaccine protection.

Early data suggests it can be resistant to vaccines and is more transmissible than the Delta variant which has only two spike proteins and was until now the dominant infection worldwide.

The WHO also warned that the low vaccination rates in regions such as Africa would provide breeding grounds for new variants such as Omicron.

The USA and Europe have in recent days seen a surge in Omicron infections.