China's COVID-19 prevention and control work has achieved success in its first phase, but phase two will last for a year or two and possibly even longer, based on the current situation, a senior expert said on Saturday.

Zeng Guang, chief epidemiologist at the Chinese Center for Disease Control and Prevention, said at a symposium that outbreaks have recently occurred in many places in China.

"If it were to continue like this, it would be an important public health issue that needs more attention," he said.

Xu Hejian, a spokesman for the Beijing municipal government, said at a news conference on Sunday that the capital still faces a complicated situation because of the occasional imported cases that infect others.

The Beijing government announced on Saturday that a Hanting Hotel in the Dashanzi area of Chaoyang district, where one confirmed imported COVID-19 patient stayed and two new related local cases were reported, has been designated as a medium-risk area.

Pang Xinghuo, deputy director of the Beijing Center for Disease Control and Prevention, said the health authority has started nucleic acid testing of all residents in nearby communities. These residents are not allowed to make unnecessary trips out of the city. Anyone who must leave the city would first have to submit a negative nucleic acid test result no older than seven days.

All restaurants, convenience stores and hairdressers are required to reduce opening hours and strictly conduct body temperature checks.

Pang said the two confirmed local cases were contacts of the imported case, a person who stayed in the hotel. They are both workers at a restaurant near the hotel and lived in the same dormitory.

Dalian, Liaoning province, said on Sunday afternoon that all of its medical institutions have entered "a state of war" for COVID-19 prevention and control.

The port city reported a new confirmed case on Saturday. A 39-year-old man tested positive while being quarantined as a close contact of a previously identified asymptomatic patient. He was owner and chef of a restaurant on a street in Jinpu New Area, said Zhao Lian, deputy director of Dalian's Health Commission.

The residential compound where the man lived was classified as a medium-risk COVID-19 area on Saturday.

After Dalian reported a new cluster of four asymptomatic cases on Tuesday, two confirmed cases were reported on Saturday, and six people with asymptomatic cases are under medical observation.

Meanwhile, Guangzhou reported on Sunday that a woman who works in a hotel assigned as a quarantine site for travelers from abroad now was an asymptomatic case, and Suifenhe, Heilongjiang province, reported three new asymptomatic cases on Saturday.