Authorities in Tianjin are sparing no efforts to stop the novel coronavirus from spreading outside the city after detecting 97 positive samples by noon on Tuesday.

Han Jinyan, deputy director of the Tianjin Health Commission, said the positive results include 49 locally transmitted cases and 15 asymptomatic carriers, with at least two having been confirmed as the Omicron strain.

There are also another 33 people who tested positive in preliminary testing and screening, with further verification needed, Han said at a news conference on Tuesday.

Ninety of the positive samples were collected from tests in Jinnan district, three in Xiqing district, three in Hexi district and one in the Binhai New Area, she said.

"The patients and asymptomatic carriers are aged between 5 and 74 years old," Han said.

The number of people with positive results in nucleic acid testing has grown quickly, with at least six cluster infections from family groups since Jan 6, she said.

As of Tuesday, the northern port city had three high-risk areas in the Xinzhuang and Xianshuigu townships in Jinnan district, Han said.

Tianjin started a citywide nucleic acid testing campaign on Sunday, with about 12 million residents having their samples collected.

Seventy-seven people had been found positive from the 7.9 million results completed by noon on Tuesday, Han said.

To curb the spread of COVID-19, Liu Daogang, deputy director of the Tianjin Municipal Transportation Commission, said trains departing from some railways stations in Tianjin have been suspended to prevent the virus from spreading to Beijing, located 130 kilometers away.

Liu said 123 bus routes linking Tianjin to other provinces, regions and municipalities, plus all intercity taxi and car-hailing services, have also been suspended.

Government departments have set up 279 checkpoints on highways to ensure only those with negative results from nucleic acid tests done within 48 hours, green health codes and certificates from their companies or neighborhoods are allowed to leave Tianjin after having their body temperature measured, Liu said, adding the strict measures are also applicable to visitors to Tianjin.