President Joe Biden has unveiled stricter Covid-19 travel rules as the US confirmed a handful of cases of the Omicron variant from coast to coast.
From next week, international travellers to the US, including Americans, must take a Covid test no more than one day before travel, regardless of vaccination status.
Those recently recovered may provide “proof of recovery” documents instead.
Mask requirements on planes, trains and buses will be extended until mid-March.
Millions of free and insurer-funded home tests will also be made available.
Ten cases of the Omicron variant have been detected in the US: in California, Colorado, Minnesota, and New York, and in Hawaii, where authorities say that person had no recent travel history.
State health officials have reported only mild symptoms in these cases.
The variant has now been found up to 30 countries, according to reports.
It is still not clear whether Omicron, a highly mutated variant, is associated with more transmission or more risk of evading vaccines.
- How worrying is the new Covid variant?
- Covid variants: Do we need new vaccines yet?
- Biden: Omicron lockdown not needed for now
The US is encouraging all adults to get booster vaccines, amid warnings Covid cases will rise this winter.
“We’re going to fight this variant with science and speed, not chaos and confusion,” Mr Biden said at the National Institutes of Health in Maryland.
He repeated earlier assurances that the plan “doesn’t include shutdowns or lockdowns”.
Over 40 million Americans have received their Covid boosters, but nearly 100 million more are eligible and have not yet had theirs, the president said.
Hundreds of family vaccination clinics will be set up across the country in an attempt to increase vaccination rates among children and teenagers.
Officials said private insurers would be obliged to reimburse their 150 million customers for at-home Covid tests they buy, and that 50 million tests would be distributed free to the uninsured through health centres and rural clinics.
However, reimbursement for tests does not begin until January, after the holiday period which sees increased travel and indoor mixing.