"We all know when you have a virus that has already gone to multiple countries, inevitably it will be here," Fauci told ABC's "This Week" anchor George Stephanopoulos. "The question is, will we be prepared for it?"
Fauci's comments came one day before the United States plans to impose a travel ban on most travelers from eight southern African countries.
MORE: What is omicron? What to know about new COVID variant
Pressed by Stephanopoulos on whether the omicron variant is as or more transmissible than the delta variant and other mutations that have swept the globe, Fauci, director of the National Institute of Allergy and Infectious Diseases and the White House's point man on the pandemic, said, "It appears to be."
"It has a bunch of mutations," Fauci said, including, "a disturbingly large number of mutations in the spike protein, which is the business end of the virus."
The omicron variant, named after the 15th letter of the Greek alphabet, was first detected last week in Botswana, officials said. Since then, cases of the new variant have been found in South Africa, Germany, Belgium and Hong Kong.
Asked by Stephanopoulos if omicron causes more severe disease, Fauci said that currently remains a mystery.
He said U.S. scientists spoke to their counterparts in South Africa on Friday and plan to meet with them again later Sunday "to try and find out if the cases they have identified that clearly are caused by this variant, what is the level of severity in that."
"Hopefully, it will be light," Fauci said.
This is a developing story. Please check back for updates.