Authorities in China's biggest city, Shanghai, have begun Wednesday a new round of nucleic acid testing for key regions as part of preventive measures against the COVID-19 pandemic.

This comes as the city is facing "the severest and complex challenge since epidemic prevention and control began on a regular basis," Wu Jinglei, director of the Shanghai Health Commission, pointed out at a Wednesday press conference. 

According to the city's health commission, Shanghai reported Tuesday four local COVID-19 cases and 977 local asymptomatic infections.

The Global Times newspaper said that "Shanghai has renovated two indoor stadiums as quarantine sites for mild COVID-19 cases and asymptomatic carriers."

In addition, authorities have required "14 days of centralized observation and seven days of self-health management" for close contact with infected people, where seven nucleic acid tests will be required during this period, the Global Times noted.

Wu Fan, a leading expert with Shanghai's COVID-19 medical team, stressed that "the city insists on a scientific, targeted and dynamic zero-COVID policy, mentioned the newspaper.

Amid the rise of COVID-19 cases in the Chinese city, several rumors have spread, claiming Shanghai will witness another lockdown.

The Global Times cited the Shanghai police as saying that "Two residents surnamed Zhang and Yu, who spread false information such as "Shanghai is going to be locked down for seven days," were put under investigation by Shanghai police on suspicion of fabricating and deliberately spreading false information, and the investigation is continuing."

It is noteworthy that the hashtag "Shanghai lockdown is rumor" recorded over 170 million clicks on China's Twitter-like Sina Weibo platform.