HARBIN -- Harbin, capital of northeast China's Heilongjiang province, has been on high alert after new local COVID-19 infections emerged on Sept 21.

The city reported eight confirmed COVID-19 cases from 6 pm Tuesday to 4 pm Wednesday, according to the city's COVID-19 prevention and control headquarters.

The cases are all close contacts of the three confirmed cases reported earlier Tuesday.

Harbin, with a population of more than 10 million, launched citywide nucleic acid testing on Tuesday afternoon and plans to complete the campaign by the end of Thursday, the headquarters said.

The city has also suspended COVID-19 vaccinations for three days in an effort to focus on the mass testing.

The headquarters encouraged local residents to stay put and avoid gatherings to reduce the risk of infection.

Harbin has tightened curbs by suspending commercial operations in relatively confined spaces and private clinics and limiting the number of visitors to local tourist sites to 50 percent of capacity.

Harbin Taiping International Airport said those who want to leave must provide a negative nucleic acid test result issued within 48 hours before their departure.