SHANGHAI, Jan 17 (Reuters) - China is doubling down on its "zero-COVID" strategy, saying the spread of the potentially milder Omicron variant is no reason to lower its guard amid warnings of economic disruptions and even public unrest as lockdowns drag into a third year. As other countries talk about a transition from "pandemic" to "endemic", China has stepped up policies to stamp out any new outbreak as soon as it arises, sealing off cities, shutting transport links and launching mass testing programmes. The approach has kept infections at a minimum, but some experts warn that China could become the victim of its own success as a lack of exposure to COVID-19 over the last two years leaves it vulnerable to the more infectious Omicron. That could prompt authorities to resort to ever more draconian measures, with more potential disruption of global supply chains, at least until a crucial autumn conclave of the ruling Communist Party, when President Xi Jinping is expected to secure a third term as China"s leader. China has "backed itself into a corner", Yanzhong Huang, a global health specialist at the Council on Foreign Relations (CFR), a U.S. think tank, told Reuters. "Beijing seems to be confident that stringent pandemic control measures will still work," said Huang. "But with a large population that does not have immunity against COVID-19, it should be easy for this new variant to quickly multiply and spread in China." China has cancelled scores of inbound international flights in recent weeks due to passenger infections. He Qinghua, a disease prevention official at China"s National Health Commission (NHC), said that while the country is under increasing strain from imported infections, it is still well-equipped to contain the virus. "Once the epidemic is discovered, it will be handled and extinguished immediately so as to ensure that the people enjoy a happy and peaceful spring festival," He told reporters on Saturday. The approach of the Lunar New Year, when hundreds of millions of people typically travel, has already led to tougher curbs in many cities. VICTIM OF SUCCESS In Shanghai, a major transit point that has seen a spike in "imported" infections in recent weeks, authorities recently sealed off office blocks, department stores and a tea shop where two people who tested positive for COVID had worked. Several schools in the city have closed early for the holiday. China has become a victim of its own success and is now struggling to find a way out, the U.S.-based Eurasia Group said in a report earlier this month. "The initial success of zero COVID-19 and Xi"s personal attachment to it makes it impossible to change course," it said. "China"s policy will fail to contain infections, leading to larger outbreaks, requiring, in turn, more severe lockdowns," it said, predicting greater economic disruptions and rising public dissatisfaction. That provoked an angry response from the official China Daily on Friday, which described it as "a ridiculous conjecture full of political bias". China"s swift development of its own vaccines was another early success that could lead to problems later. China was able to vaccinate its huge population quickly while many other countries were still vying for supplies, but studies suggest its shots may not be as effective against Omicron as the mRNA vaccines used widely in the West. Wall Street bank Goldman Sachs said just 10% of its China-based clients believed the "zero-COVID policy" would ease in coming months. Chinese officials have intensified the drumbeat of warnings. Omicron is "faster and stealthier compared to Delta, but still has a destructive power that cannot easily be ignored," said Zhang Wenhong, who leads a Shanghai team of experts on COVID-19 treatment, in comments posted on his Weibo microblog. Social media users voiced frustration over tightening rules in the run-up to the holiday. One Shanghai resident "almost didn"t dare to leave home" because of the recent lockdowns, she wrote on Weibo. "Highlighting the risk posed by the new variant helps sustain the fear among the public, which justifies the continuation of the zero-COVID policy," said CFR"s Huang. "But it also makes it even more difficult for China to implement an exit strategy."