Passengers of China-bound flights must provide negative COVID-19 test results before boarding, China's aviation authority said Tuesday, as the government looks to further reduce the risk of imported coronavirus cases amid increased international travel.

Nucleic acid tests must be completed within five days of embarkation, the Civil Aviation Administration of China (CAAC) said on its website. Tests should be conducted at facilities designated or recognized by Chinese embassies in host countries, it said.

The embassies will carefully assess the testing capacity of host countries and formulate travel procedures when testing conditions are met, CAAC said.

The announcement comes as countries struggle with testing capacity and speed. In parts of the U.S., receipt of test results can take up to two weeks, while in some other countries, nucleic acid tests are reserved for people who have come in close contact with COVID-19 patients or who have symptoms of the potentially fatal disease.

In the past month, CAAC has allowed more foreign airlines to resume services in China and add flights to the country as the economy recovers. Deutsche Lufthansa AG said Friday it would double the number of flights to and from mainland China in coming weeks, and Air France KLM SA said it has received approval to add more China flights.

A number of airlines have been suspended from operating China routes after more than five passengers tested positive for the coronavirus upon arrival.