The United States will soon require international travelers entering the country to take a Covid test one day prior to departure, regardless of vaccination status, an official said Wednesday amid global concern over the Omicron variant.

A spokesperson for the Centers for Disease Control and Prevention (CDC) said the measure would be announced once the rule is finalized. 

President Joe Biden is set to talk about America's winter plans for Covid on Thursday and might announce the new requirements then. 

Currently, vaccinated travelers to the United States require a test three days prior to departure. Unvaccinated Americans or permanent residents need a test within one day, while unvaccinated non-citizens may not enter by air, with few exceptions.

The agency is also evaluating "considerations around additional post-arrival testing and self-quarantines," CDC Director Rochelle Walensky said at a briefing Tuesday. 

Citing three federal officials, the Washington Post reported the government is weighing a proposal to require all travelers get retested within three-to-five days of arrival, which is currently only a recommendation.

More controversially, they are also debating a proposal to oblige travelers, including US citizens, to self-quarantine for seven days even if their test results are negative. 

"Those who flout the requirements might be subject to fines and penalties, the first time such penalties would be linked to testing and quarantine measures for travelers in the United States," the newspaper reported. 

The moves come just weeks after the country relaxed travel restrictions from more than 30 countries and instituted a two-tier testing approach based on vaccination status.

It comes amid fears over the potential dangers of Omicron, the variant first reported in South Africa but now prevalent in more than 20 countries.

Scientists do not yet have hard data, but based on the variant's pattern of mutations expect it will at least partly evade the protective action of current vaccines, and may be more transmissible than Delta, the currently dominant strain.