BEIJING, Jan 13 (Reuters) - China"s northern 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 city. Omicron has brought new challenges for China"s strategy to quickly stamp out outbreaks, which has taken on urgency ahead of the Winter Olympics set to start from Feb. 4, while the busy Lunar New Year travel season begins this month. Volkswagen Group"s (VOWG_p.DE) China unit said it had shut a vehicle plant run jointly with FAW Group in Tianjin, as well as a component factory since Monday due to the outbreak. read more Tianjin, located about 100 km (62 miles) from the capital Beijing, reported 41 domestically transmitted infections with confirmed symptoms on Wednesday, up from 33 a day earlier, National Health Commission data showed. Dalian in the northeast also reported an individual arriving from Tianjin had tested positive for Omicron, city officials said. It said the virus situation was "largely controllable". Anyang in the central province of Henan reported 43 local symptomatic cases on Wednesday, after two Omicron infections on Monday. It traced the flare-up to a student from Tianjin. read more Case numbers in Tianjin and Anyang are tiny compared with outbreaks in many other countries, though the number of local Omicron infections is unclear. Still, officials imposed curbs on movement within the cities and outside. Several cities across China have ordered quarantine for recent visitors to the two cities. Beijing is among the many cities urging people to stay put during the Lunar New Year holiday. Citing the Omicron risk and the need to keep the Olympics Games safe, officials in the capital encouraged commuters from satellite towns to work from home. An aerial view shows people lining up at a nucleic acid testing site during the second round of mass testing for the coronavirus disease (COVID-19), after local cases of the Omicron variant were detected in Tianjin, China January 12, 2022. Picture taken January 12, 2022 with a drone. China Daily via REUTERS People line up at a nucleic acid testing site during the second round of mass testing for the coronavirus disease (COVID-19), after local cases of the Omicron variant were detected in Tianjin, China January 12, 2022. Picture taken January 12, 2022. China Daily via REUTERS Community workers sort vegetables to be distributed to residents of an area under lockdown following the coronavirus disease (COVID-19) outbreak in Tianjin, where the Omicron variant has been detected, China January 12, 2022. Picture taken January 12, 2022. cnsphoto via REUTERS 1/3 People line up at a nucleic acid testing site during the second round of mass testing for the coronavirus disease (COVID-19), after local cases of the Omicron variant were detected in Tianjin, China January 12, 2022. Picture taken January 12, 2022. China Daily via REUTERS There were no new deaths on Wednesday, leaving the toll since the virus was first found two years ago in China unchanged at 4,636. IMPORTED INFECTIONS Zhang Wenhong, director of a COVID-19 treatment team in Shanghai, said on Thursday the public health clinic in the commercial hub faced a record number of infections arriving from overseas. Imported cases in Shanghai during the first 10 days of this month have already exceeded December"s total, Reuters calculations showed. How many were caused by Omicron is unclear. China has suspended more U.S. flights after a surge in numbers of infected passengers. Its tough measures against local outbreaks included punishment for officials, with 11 people held to account in Anyang by Wednesday for failing to properly control the virus. On Thursday, city authorities in the ancient town of Xian ordered two hospitals to suspend operations for three months for failures in providing medical care during the outbreak. The move drove down shares of their owner, XiAn International Medical Investment Co (000516.SZ), by 10%, or the maximum permitted daily percentage change. One of the hospitals apologised for rigid virus controls that delayed treatment for a patient who suffered a heart attack and died. The story of a pregnant woman who lost her unborn baby after waiting for two hours outside the other hospital provoked anger on Chinese social media and brought punishment for city officials. read more