The United States and Australia became the latest countries to confirm locally transmitted cases of the variant, as Omicron infections pushed South Africa's total cases past three million.
The health agency said that it has warned it could take weeks to determine how infections the variant is, whether it causes more severe illness and how effective treatments and vaccines are against it.
WHO emergencies director Michael Ryan said that they are going to get the answers that everybody out there needs.
However, no deaths have been reported related to Omicron, WHO said but the new variants spread has led to warnings that it could cause more than half of Europe's Covid cases in the next few months.
Meanwhile, International Monetary Fund chief Kristalina Georgieva said that the new variant of COVID-19 could also slow global economic recovery.
A preliminary study by researchers in South Africa, where the variant was first reported on November 24, suggests it is three times more likely to cause reinfections compared to the Delta or Beta strains.