The Chinese mainland reported on Monday its first case of the highly transmissible Omicron COVID-19 variant in Tianjin as authorities in Zhejiang province stepped up measures to control outbreaks of the Delta strain.

The Tianjin Health Commission reported on Monday an imported asymptomatic patient, who was later confirmed to be infected with the Omicron variant. The carrier arrived in the city on Thursday, the commission said.

In another development, three cities in Zhejiang－Ningbo, Hangzhou and Shaoxing－reported 192 confirmed COVID-19 cases and one asymptomatic case between Dec 5 and 4 pm on Monday, health officials said.

More than 9.45 million people in the three cities have so far received nucleic acid tests. Over 7.2 million people have tested negative for the virus.

Provincial health authorities have asked the cities' authorities to step up nucleic acid testing for at-risk people and make the utmost efforts to contain the outbreak. They also urged members of the public to strictly follow epidemic control measures as New Year's Day and Spring Festival draw closer.

Hu Jialin, deputy director of the Zhejiang Department of Transportation, said that the entrances and exits of five expressways in the province have been closed. All seaports in Zhejiang are operating normally, with the exception of the port area in Ningbo's Zhenhai district, which has been closed due to the outbreak.

Shaoxing, a city in northern Zhejiang, reported 123 confirmed cases and one asymptomatic case as of 4 pm on Monday. Most cases were in the city's Shangyu district, which imposed a lockdown on Saturday afternoon. According to the city's health authorities, multiple cases were reported on Sunday at the Xindatong Supermarket, a fresh food mart in the district.

Three temporary laboratories were put into use in Shangyu on Monday to improve nucleic acid testing capacity, Sun Liming, deputy director of the provincial health commission, said on Monday. The three laboratories have the capacity to test 5 million people over a 24-hour period.

A total of 18 cases have been reported in Hangzhou over the past eight days, health authorities said.

The total number of confirmed COVID-19 cases on the mainland had reached 99,780 by Sunday, including 1,381 patients still receiving treatment, the National Health Commission said in its daily report on Monday. Twenty-seven patients were in severe condition, the commission said.

Fang Xiaoying in Hangzhou contributed to this story.