WASHINGTON -- By early next week, Canadians and all other foreign visitors who travel to the United States by air will need to get a COVID-19 test no later than the day before their departure.

U.S. President Joe Biden is slashing the current 72-hour testing window for fully vaccinated travellers as part of a suite of public health measures aimed at slowing the spread of the highly mutated Omicron variant.

A White House background briefing on the plan late Wednesday made no mention of land borders, or whether fully vaccinated Canadians who drive south would be required to show a test result.

The rise of Omicron marks only the latest twist in the long road back to some semblance of normality for people who routinely travel back and forth between the two countries.

It's been less than a month since the U.S. lifted its restrictions on fully vaccinated non-essential travellers seeking to enter the country by land from Canada and Mexico.

Canada, meanwhile, has for now exempted U.S. visitors from its stringent new rules, which require all other foreign air travellers to get tested upon arrival and self-isolate while awaiting the results.