Shanghai reported three locally transmitted COVID-19 cases on Thursday, after nearly four months of no new local coronavirus infections in the city.

The three infected people had traveled to neighboring Suzhou, Jiangsu province, in the past week, Shanghai's top health official said at a media briefing.

"So far, there has been no evidence to show whether the cases are related to other local infections in the country. The city's disease control professionals are racing against time to proceed with in-depth epidemiological investigations and origin tracing," said Wu Jinglei, director of the Shanghai Health Commission.

The three infected women are all friends. The first two traveled to Suzhou from Friday to Sunday, and the third joined them on the last day of the trip.

All three have been transferred to a hospital designated for COVID-19 treatment and on Thursday were in stable and good condition, Wu said.

The first patient is a 34-year-old resident of Xiamen, Fujian province. She traveled from Xiamen to Beijing on Nov 12 and arrived in Shanghai on Nov 15 and stayed at a residential community in Pudong district.

The second woman, 32, lives in Pudong's town of Sanlin, and the third is a 31-year-old resident of Zhaoxiang, Qingpu district, who was located through contact tracing.

Shanghai Center for Disease Control workers have traced 27 close contacts of the three women in Shanghai, 103 secondary close contacts and more than 10,600 individuals related to the cases. As of 5 pm on Thursday, all nucleic acid tests from contacts had shown negative results.

The three residential communities where the infections were traced to have been designated as medium-level risk areas for COVID-19 and on Thursday were placed under closed-loop management, which restricts the movement of residents.

Zhang Wenhong, director of the infectious diseases department at Huashan Hospital Affiliated with Fudan University, said unexpected waves of infections may become normal in winter.

"CDC workers have experience in getting the virus' spread under control in the shortest time possible, while having the least influence on residents' daily lives," said Zhang.

"Our country is still sticking to the strategy of rapid response and precise prevention and control," he added.

Meanwhile, Hangzhou, Zhejiang province, reported two new COVID-19 cases, local health authorities said on Thursday night.

The two patients, surnamed Qu and Zhu, had traveled outside the city and returned to Hangzhou on Monday. They were later diagnosed as having asymptomatic COVID-19 and were sent to designated hospitals for treatment.

One of the two works at Zhejiang University Museum of Art and Archaeology, which is on Zhejiang University's Zijingang Campus.

The museum and the campus were closed on Thursday afternoon, the university said.

Xuzhou, in Jiangsu, also reported an asymptomatic COVID-19 case on Thursday night, according to local authorities. That patient had eaten a meal on Saturday at a restaurant where the confirmed patients from Shanghai had eaten on the same day.