The heavily mutated Omicron coronavirus variant is likely to spread internationally and poses a very high risk of infection surges that could have "severe consequences" in some places, the World Health Organisation (WHO) has said.

In anticipation of increased case numbers as the variant, first reported last week, spreads, the UN agency urged its 194 member states to accelerate vaccination of high-priority groups and ensure plans were in place to maintain health services.

"Omicron has an unprecedented number of spike mutations, some of which are concerning for their potential impact on the trajectory of the pandemic," the WHO said.

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