The World Health Organization says the Omicron coronavirus variant is likely to spread internationally, posing a "very high" global risk of infections that could have "severe consequences" some areas.
On Monday, the UN agency urged its 194 member states to accelerate vaccination of high-priority groups and, in anticipation of increased case numbers, to "ensure mitigation plans are in place" to maintain essential 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.
"The overall global risk related to the new variant ... is assessed as very high."
To date, no deaths linked to Omicron have been reported, though further research is needed to assess Omicron's potential to bypass immunity created by vaccines and previous infections.
"Increasing cases, regardless of a change in severity, may pose overwhelming demands on health care systems and may lead to increased morbidity and mortality. The impact on vulnerable populations would be substantial, particularly in countries with low vaccination coverage," it said.
Variant spreading rapidly worldwide
The variant was first reported to the WHO on 24th of November from South Africa, where infections have risen steeply.
It has since spread around the world, with new cases identified in the Netherlands, Denmark and Australia even as more countries imposed travel restrictions to try to seal themselves off.
Japan said on Monday it would close its borders to foreigners, joining Israel in taking the toughest measures.
Meanwhile, French authorities are waiting for laboratory confirmation of eight suspected cases of the Omicron variant, involving people who traveled recently to southern Africa
The WHO, in its latest guidance, reiterated that countries should use a "risk-based approach to adjust international travel measures in a timely manner".
Overall, there are considerable uncertainties in the magnitude of Omicron's impact on vaccinated people.
More data is expected in coming weeks.