Required masks on public transportation, including airplanes, rails and buses, will be extended through March 18, according to a new plan from the Biden administration.

Tighter requirements for travel into the U.S. will go into place early next week, the administration said. The rule calls for proof of a negative test within one day of travel to the U.S. for all passengers, regardless of their vaccination status or nationality.

President Joe Biden also announced a plan Thursday allowing for free rapid tests.

Senior administration officials say the more than 150 million Americans with private insurance will be able to submit for reimbursement to their insurance companies through the same rule that allows tests on site to be covered by insurance. To reach uninsured Americans and those on Medicare or Medicaid, the Biden administration will send 50 million at-home tests to 20,000 federal sites around the country to be handed out for free.

The Department of Health and Human Services, Department of Labor and Treasury Department will put out guidance by Jan. 15 to determine exactly how many tests will be covered and at what frequency, the plan said, and it will not retroactively cover tests already purchased.

-ABC News' Cheyenne Haslett, Justin Gomez

The Centers for Disease Control and Prevention is directing airlines to provide the agency with the names and contact information of passengers who have entered the United States since Nov. 29 and had been in southern Africa the prior two weeks. Airlines must turn the information over within 24 hours of the flight's arrival into the U.S.

The directive, in effect indefinitely, applies to travelers from the Republic of Botswana, the Kingdom of Eswatini, the Kingdom of Lesotho, the Republic of Malawi, the Republic of Mozambique, the Republic of Namibia, the Republic of South Africa and the Republic of Zimbabwe.

The order, which does not mention the omicron variant specifically, is to "prevent the importation and spread of a communicable disease of public health importance."

Delta and United are currently the only two carriers that offer flights between the U.S. and countries covered by the CDC order.

ABC News' Cheyenne Haslett, Sam Sweeney and Mina Kaji

Gov. Gavin Newsom said the first detected case of the omicron variant in the U.S. being found in California "is not surprising" due to the state's "aggressive testing protocols" and genomic sequencing.

During a previously scheduled press briefing Wednesday afternoon, he shared a timeline on the San Francisco resident who tested positive for the case. The person left South Africa on Nov. 21 and landed in the U.S. on Nov. 22, developed symptoms a few days later around Nov. 25 and got tested on Nov. 28, he said. The test came back positive on Nov. 29, he said.

On Nov. 30, initial lab testing determined the sample could be omicron, and a full sequencing confirmed it was early Wednesday morning, San Francisco health officials said.

Newsom encouraged Californians to get vaccinated and receive a booster shot as the winter approaches.

The individual who tested positive for the first case of the omicron variant detected in the U.S. had received a full dose of the Moderna COVID-19 vaccine but was not yet eligible for a booster dose, according to San Francisco Department of Public Health Director Dr. Grant Colfax.

The person developed symptoms upon returning from South Africa, got tested in San Francisco and has since recovered, Colfax told reporters during a briefing Wednesday.

"They did the right thing and got tested and reported their travel history," he said.

Colfax said the case is "not a cause for us to panic," and that San Francisco "is prepared" for this.

The health department has no plans at this time to change its current COVID-19 health orders, Colfax said.