All residents of Dalian, Liaoning province, are to receive nucleic acid tests after recent cases of COVID-19 have been reported, local health officials said on Tuesday.

The latest round of tests, which started at noon on Tuesday, is expected to cover all residents within three days.

Residents have been told not to leave the city unless it is necessary, and those who do need to leave must first provide a negative nucleic acid test result no older than seven days.

From Dec 15 through Monday, the city reported five confirmed, domestically transmitted COVID-19 cases and 12 asymptomatic, domestically transmitted cases, officials said. On Monday alone, there were two new confirmed cases and six new asymptomatic cases.

On Dec 16, local authorities had reported that four cold storage enterprise workers in Dalian who showed no symptoms had tested positive for COVID-19.

The asymptomatic cases were detected when workers with the Dalian Port Yidu Cold Chain Co were undergoing regular nucleic acid testing the day before, according to the municipal COVID-19 prevention and control headquarters.

The city has been carrying out large-scale nucleic acid testing and screening in its Jinpu New Areawhere most of the cases were detected－as well as in Pulandian district and Dalianwan area.

Residents of downtown areas like Zhongshan district will now be given nucleic acid tests, while residents of some key areas are getting multiple coronavirus tests to ensure all cases are caught.

Jinpu New Area will have a second round of tests and some in other key communities will have a third round of tests, said Zhao Lian, deputy director of Dalian's health commission, at a news conference on Tuesday.

Wang Jie, deputy director of the administrative committee of Jinpu New Area, said Jinpu has been carrying out rapid testing covering all residents, with an emphasis on tests in key areas to quickly cut off further potential transmissions.

As part of the large-scale screening efforts that followed the initial reports, around 1.25 million people have been tested in Jinpu New Area, 111,344 were tested in the Dalianwan area and 60,335 tested in Pulandian.

All of those results came back negative, Zhao said.

Two residential compounds in Jinpu New Area have been classified as medium-risk zones for COVID-19, Zhao said.

To assist in the virus control effort, more than 100 medical workers and other related staff from around Liaoning province have been dispatched to Dalian to help with tasks like contact tracing, Zhao said.

There also are 26 designated quarantine hotels in Jinpu, where 2,013 people are under quarantine.

Xinhua contributed to this story.