SHANGHAI, Jan 14 (Reuters) - China suspended dozens of international flights on Friday amid a global surge in Omicron cases, while the city of Shanghai curbed tourist activity as it rushed to head off local COVID-19 infections as imported cases rose. Cities across China are becoming more vigilant against COVID-19 ahead of the Lunar New Year travel season later this month and as Beijing readies to stage the Winter Olympics beginning Feb. 4, with many local governments urging residents not to leave town unnecessarily. Shanghai"s tourism and culture authority said travel agencies and online tourism companies must once again halt organising group tours into and out of Shanghai after it reported five new domestically transmitted infections on Thursday, all linked to an arrival from overseas. The order, in line with a national guideline to cut tourist activities in provinces where new infections have emerged, came less than a month after Shanghai lifted a suspension that had come into effect in November. Late on Friday, Zhuhai city in the southern Guangdong province found seven coronavirus infections during testing schemes in local areas, with the Omicron variant detected according to preliminary sequencing result, state television said, without saying exactly how many of the seven cases were Omicron. Earlier on Friday, Zhuhai suspended all flights to the capital Beijing city. China has dramatically cut back on international arrivals during the pandemic, but the number of infected travellers arriving in Shanghai, a major financial hub, during the first 10 days of January, exceeded those for all of December. China has reported local transmissions of the highly-contagious Omicron variant in the northern city of Tianjin and three other provinces but has not said how many Omicron cases it has detected in total. Authorities, however, have warned that Omicron adds to the increased risk of COVID-19 transmission as more people return to China from overseas for the Lunar New Year holiday. China on Friday announced that 30 inbound international flights from several countries were suspended due to COVID-19 cases, including four more from the United States. So far this year, China has announced the cancellation of 74 flights from the United States. read more Athletes and other personnel involved in the Olympics are arriving largely on special charter flights and immediately entering a strictly enforced "closed loop" that separates them from the wider population. read more Unlike some other Chinese cities, Shanghai has largely refrained from broader curbs that risk disrupting normal routines and has taken a more surgical approach. This week it raised the "virus risk" level only for a small bubble tea shop where three of the five local infected people worked. MORE QUARANTINE ROOMS China reported a total of 143 local confirmed cases, and four domestically transmitted asymptomatic carriers for Jan. 13. Most new cases were detected in the central province of Henan, where both the Omicron and Delta variants are spreading, and in Tianjin. Although China"s caseload remains tiny compared to outbreaks elsewhere, the country aims to stamp out local clusters as quickly as possible, an approach that has forced local governments to rapidly isolate the infected as well as their close contacts. This week, hundreds of thousands of people were quarantined in centralised facilities or at home in China"s worst-hit cities. The city of Yuzhou in Henan started building another 6,000 makeshift quarantine rooms on Friday after its mayor said the more than 1,000 rooms currently available were "still not enough", according to state media. Zhengzhou, Henan"s capital, is speeding up preparation for 5,000 quarantine rooms which it aims to make ready by April, a local official said this week.