The fight against the COVID-19 outbreak in East China's Zhejiang province has entered "the most critical period", a top provincial health official said on Thursday.

Sun Liming, deputy director of the Zhejiang Provincial Health Commission, told a news conference Zhejiang has been working around the clock to meet the target of "keeping the epidemic within the province and reducing the number of infections to zero" through all-around management and control measures and smart governance.

Zhejiang reported 50 new cases on Thursday, bringing the total number of COVID-19 cases in the latest outbreak to 343. Shaoxing, the hardest-hit city in Zhejiang, reported 45 new cases on Thursday, with three new cases in Hangzhou, the provincial capital, and two in Ningbo.

The risk level for COVID-19 in five areas in Shaoxing's Shangyu district was raised to the highest level on Wednesday.

Among the five high-risk areas, the Datong Supermarket has reported a cluster of over 50 cases, with nearly 40 percent of the patients over 60 years old. In Ningbo, around half of those infected have been over 60.

"This may have something to do with senior people's relatively low capabilities in using new technologies such as smartphones and electronic payment systems," Wu Anhua, chief expert at the Infection Control Center of Xiangya Hospital Central South University, told Health Times. "Many of them still prefer to use cash when shopping, which might also pose difficulties for epidemiological tracing after the outbreak occurred."

Wu said checking health codes and measuring body temperatures should be mandatory for those who enter places such as fresh food supermarkets and shopping centers.

Zhang Jianmin, chief physician at Tongde Hospital in Hangzhou, said on Thursday that residents who are still in closed-loop management should pay close attention to their physical health, cooperate with doctors if they have any symptoms, frequently communicate with family and friends through social networks, and call the official hotline to seek psychological counseling if necessary.

Fang Xiaoying in Hangzhou contributed to this story.