A medical worker collects a swab sample for nucleic acid testing at a testing site in a community in Siming District, Xiamen, southeast China's Fujian Province, Sept. 14, 2021. (Photo by Zeng Demeng/Xinhua)

China has updated its protocol on mass testing to better respond to possible COVID-19 resurgence caused by the highly transmissible Delta variant.

Suppose mass nucleic acid testing needs to be carried out in a city with more than 5 million people. In that case, it shall be completed within three days, according to the updated protocol from the National Health Commission.

The time limit was set at three to five days for cities of the same size in the previous version of the protocol introduced in February this year.

For cities with less than 5 million people, the time limit for completing city-wide testing remains unchanged at two days.

When necessary, cities with a population of more than 5 million can apply for national assistance to complete the testing within the time frame, according to the updated protocol.

The update aims to enhance further China's ability to organize and implement mass nucleic acid testing and see that the country can effectively cope with any possible COVID-19 resurgence caused by the Delta variant, it says.