The United States will start reimposing mandatory COVID-19 tests for all air travelers from China, authorities announced Wednesday.

From Jan. 5, "all air passengers two years and older originating from China will be required to get a test no more than two days before their departure from China, Hong Kong and Macau, and show a negative test result to the airlines upon departure," a federal health official said.

"The recent rapid increase in Covid-19 transmission in China increases the potential for new variants emerging," the official told reporters in a phone briefing.

However, the official said, Beijing has provided only limited data about circulating variants in China to global databases, and testing and reporting on new cases has also diminished.

"Based on this lack of available data, it's harder for US public health officials to identify new variants spreading to the United States," the official said.

"The United States is taking deliberative proactive steps to protect Americans' public health, and be on alert for any potential Covid-19 variants emerging," the official said.

The new requirement will fall into place just after midnight U.S. Eastern Time on Jan. 5, or 0500 GMT.

The test requirement applies to air passengers regardless of nationality and vaccination status and includes people traveling to the United States from China via third countries, as well as those traveling through the United States to other countries.