Biden, who is spending Thanksgiving with his family in Nantucket, Massachusetts, told reporters on Friday, “We don’t know a lot about the variant except that it is of great concern, seems to spread rapidly.”

Omicron was first detected in South Africa this week, leading countries around the globe, including the US, to impose travel restrictions on the southern African nation and at least seven others in the region.

No cases of Omicron have been identified in the US to date, the Centers for Disease Control and Prevention said on Friday. The agency expects that it would identify the variant quickly, if it emerges in the US.

But Dr Anthony Fauci, the nation’s top infectious disease specialist, said on NBC’s “Weekend TODAY” show on Saturday, “I would not be surprised if it is.”

“When you have a virus that is showing this degree of transmissibility and you’re already having travel-related cases that they’ve noted in Israel and Belgium and other places, when you have a virus like this, it almost invariably is ultimately going to go essentially all over,” Fauci said.

The vice-president told reporters on Saturday that the administration will take it “one step at a time”, when asked about additional travel restrictions. “For now we’ve done what we think is necessary,” Harris said.

The White House said senior health officials and its Covid response team have been monitoring the latest updates on Omicron and have been in regular touch with health officials around the world.