China has tightened quarantine and testing rules for incoming travelers, especially those from India and some neighboring countries experiencing surging COVID-19 cases, as the virus is mutating more rapidly and new strains are spreading faster worldwide, officials said on Friday.

He Qinghua, an official with the National Health Commission's disease prevention and control bureau, said all passengers arriving in China from overseas must be quarantined for 14 days at centralized facilities, particularly those returning from India and other neighboring countries hit hard by the virus.

For all returnees from overseas, two nasal swab samples will be collected from each person on the last day of their quarantine. "The two samples will be handled by different testing agencies and tested against two different nucleic acid reagents, which is aimed at ensuring the high quality of our tests," he said.

As incoming travelers are also required to monitor their health condition at home for seven days following the quarantine, He said timely information sharing should be stepped up among authorities across regions, in order to guarantee closed-loop management of these travelers.

He also noted variants of the COVID-19 virus are developing faster, as they have been found in an increasing number of countries. He quoted the World Health Organization's data as saying the rate of virus mutation has risen from 0.1 per one thousand to 1.3 per one thousand.

In China, new strains that first emerged in the United Kingdom, South Africa, Brazil and India have all been registered. The country had reported 142 imported infections in May as of Thursday, with a rising share of cases linked to variants, according to the commission.

Early on Wednesday, the eastern province of Anhui reported a domestic case — the first locally transmitted infection in more than three weeks. The province reported two more domestic cases as of Thursday morning, including one likely to have come in contact with incoming travelers earlier this month, the local government said.

He said more variants will surface in the future and China is capable of detecting them. "Monitoring virus mutations will be ramped up," he said. "We will analyze genome sequences of all confirmed infections and intensify tracking of virus mutations to evaluate risks promptly."