WASHINGTON/BEIJING, Jan 10 (Reuters) - China has ordered the cancellation of more than two dozen scheduled flights from the United States in recent weeks after numerous passengers tested positive for COVID-19 after arriving in China. China"s aviation regulator has mandated the cancellations of eight total scheduled U.S. passenger airline flights for Shanghai under its COVID-19 pandemic rules: four by United Airlines and two each from Delta Air Lines (DAL.N) and American Airlines (AAL.O). Delta said it canceled Detroit to Shanghai flights last Friday and Jan. 14 due to the Chinese rule requiring "all affected carriers", whose passengers test positive for COVID-19, "to cancel inbound service on certain China flights." The Civil Aviation Administration of China (CAAC) has also canceled at least 22 other U.S. bound flights operated by Chinese carriers since December after positive COVID-19 tests, including eight by China Southern Airlines Co (600029.SS). The United States is facing a surge in infections caused by the highly contagious Omicron variant and on Monday had 132,646 people hospitalized with COVID, surpassing the record of 132,051 set in January 2021. The seven-day average for new cases has doubled in the last 10 days to 704,000. United said it had been forced to cancel flights from San Francisco to Shanghai scheduled for Jan. 15, 19, 22 and 26. The Chicago-based carrier flies from San Francisco to Shanghai four times weekly. The U.S. Transportation Department (USDOT) did not immediately comment late Monday. U.S.-CHINA AIR SERVICES Since the COVID-19 pandemic, China and the United States have sparred over air services. In August, USDOT limited four flights from Chinese carriers to 40% passenger capacity for four weeks after Beijing imposed identical limits on four United Airlines flights. China told United in August it was imposing curbs on some flights after it alleged five passengers who traveled from San Francisco to Shanghai tested positive for COVID-19 on July 21. USDOT said in August that China"s policy "places undue culpability on carriers with respect to travelers that test positive for COVID-19 after their arrival in China." The department said carriers "have no means to independently verify positive test results alleged by Chinese authorities." A long-standing U.S.-China air agreement allows the countries to operate over 100 weekly flights between the two nations but only a fraction of those are currently operating. Former U.S. President Donald Trump in January 2020 barred nearly all non-U.S. citizens who had been in China within the last 14 days from traveling to the United States. President Joe Biden in November lifted the Chinese travel restrictions for fully vaccinated foreign air travelers.