The Chinese port city of Tianjin reported an increase in COVID-19 infections on Thursday as it stepped up efforts to rein in an outbreak that has spread the highly transmissible Omicron variant to another Chinese city.

Omicron has brought fresh challenges to China's strategy to quickly extinguish local outbreaks, which has taken on greater urgency in the run-up to the Winter Olympics starting on Feb. 4, with the busy Lunar New Year holiday travel season beginning later this month as well.

Tianjin, in northern China around 100 km (62 miles) from capital Beijing, reported 41 domestically transmitted infections with confirmed symptoms on Wednesday, up from 33 a day earlier, data from the National Health Commission showed on Thursday.

Dalian in the northeast also reported an individual arriving from Tianjin had tested positive for the Omicron variant, the city's government said late on Wednesday.

Dalian, which registered two local asymptomatic cases on Wednesday, said the virus situation was "largely controllable".

Anyang in central China's Henan province reported 43 local symptomatic cases on Wednesday compared with 65 a day earlier. The city detected two Omicron infections on Monday and said the flare-up could be traced to a student arriving from Tianjin. 

Case numbers in Tianjin and Anyang are tiny compared with outbreaks in many other countries, although the number of local Omicron infections is unclear. Still, officials imposed varying restrictions on movement within the cities and out of town.

Across China, several cities have ordered quarantine for people who have recently visited Tianjin or Anyang. Many cities, including Beijing, are also encouraging people to stay put during the Lunar New Year holiday.

Citing the risk posed by Omicron and the need to ensure the Olympics Games are safe, the Beijing city government also encouraged commuters from satellite towns to work from home in a statement issued on Thursday.

Imported infections

Zhang Wenhong, director of an expert team on COVID-19 treatment in Shanghai, said on Thursday the public health clinic in the city was also now facing a record number of infections arriving from overseas.

Imported cases arriving in Shanghai during the first 10 days of this month have already exceeded the total for the whole of December, Reuters calculations based on the Shanghai health authority's daily tally showed. It remains unclear how many of those were Omicron.

China has suspended more U.S. flights after a surge in infected passengers. It also required travellers from the United States to complete a nucleic acid test seven days before departure and submit their daily body temperature report for the week, on top of existing requirements. 

In Henan's Xuchang city, which is battling an outbreak of the Delta variant, local police said an official at a unit of Guangzhou Kingmed Diagnostics Group had violated the law on infectious disease control, without providing details.

Kingmed Diagnostics, whose unit had participated in a local testing programme during the Xuchang outbreak, said on Wednesday it would cooperate with the police investigation.

It said the official had helped arrange work in the city of Yuzhou, which is under Xuchang's jurisdiction, but didn't work on the testing in the lab.