The northeastern Chinese city of Dalian will undertake a second round of testing on residents in high-risk areas, following the resurgence of COVID-19.

The city has been going all out to tame the new cluster of infections since a 58-year-old man working with Dalian Kaiyang World Seafood Co. Ltd. tested positive for COVID-19 on June 22.

"A total of 21,999 medics have been mobilized to conduct nucleic acid tests at 4,297 testing sites across the city, with 4.09 million samples collected by midnight Wednesday," said Zhao Lian, deputy director of the municipal health commission.

The large-scale testing was nearing an end, Zhao said.

A total of 1,322 kindergartens have been closed since July 24 and 2,046 after-school training institutions suspended offline classes from July 23, said Zhao Yang, director of the municipal education bureau.

From June 22 to Wednesday, Dalian reported 57 locally transmitted cases, all of which are undergoing treatment in the Sixth People's Hospital of Dalian.