A new cluster of COVID-19 cases in Beijing has involved a wider range of areas and more people with its fast spread, adding difficulties to the capital's epidemic control and prevention, a senior official said on Thursday.

Beijing is facing a severe and complicated epidemic control and prevention situation that requires the departments involved to act with speed and precision to reduce transmission of the virus-that was the consensus at a meeting of the city's top epidemic control and prevention work group hosted by Beijing's Party Secretary Cai Qi on Thursday morning.

Unlike the last outbreak in the city, in which every case was linked to a tour group that traveled to the Inner Mongolia autonomous region, the new cases in Beijing are all related to a conference held in the city.

Beijing reported six locally transmitted cases and one asymptomatic case on Thursday and many of the patients are employees of PetroChina Co, which is headquartered in the capital, said Pang Xinghuo, deputy director of the Beijing Center for Disease Control and Prevention.

Those employees had been to a company conference in Beijing between Oct 28 and Wednesday. A participant in the conference was later confirmed in Jilin province to be infected with COVID-19.

"Beijing took immediate action once it learned of the confirmed case involving someone who traveled to Beijing from Jilin for the conference," Xu Hejian, a spokesman for the Beijing municipal government, said at a news conference on Thursday afternoon.

Authorities started mass nucleic acid testing for all close contacts of the confirmed patient and related areas starting on Wednesday night, he said.

One of the employees lives in a residential community in Haidian district, and her family members-her husband, daughter, mother-in-law and father-in-law-were infected with the virus.

The community was designated as a medium-level risk area for COVID-19 on Thursday.

Wang Dan, a community worker who from 1 am until 9:30 am Thursday helped organize the testing, said all the residents have shown understanding and support for the control measures.

"It's cold outside, but the testing process has been smooth and efficient," she said. "There are many volunteers working with us."

A resident surnamed Wang completed his sample collection within a few seconds.

"We will fully cooperate with all the measures," he said.

After the residential building was closed to the outside early Thursday morning, many people ordered food and daily supplies online, causing a pileup of packages outside the gate of the community.

Delivery companies have added workers to help the area.

All PetroChina institutions and subsidiaries in Beijing have been placed under a state of emergency in response to the outbreak, and all employees are being required to be tested for the virus for three successive days. As of noon on Thursday, all test results were negative.

To reduce the risk of new infections, Beijing is requiring that conferences that can be held online should do so.

Wu Yuexuan contributed to this story.