QINGDAO -- Over 7.5 million people had been sampled for nucleic acid testing by 9:30 am Wednesday in East China's Qingdao city, after it began a city-wide testing campaign on Monday.

Over 4.06 million of the collected samples have been tested so far and, with the exception of the cases already reported, no new positive samples have been detected, the municipal health commission said.

Qingdao has reported 12 new confirmed cases of COVID-19 since the virus re-emerged in the city over the weekend, the municipal health commission said.

Qingdao has a population of more than 11 million. The city has vowed to complete city-wide nucleic acid testing within five days starting from Monday.