Beijing has tightened the COVID-19 epidemic control and prevention measures to curb the virus spread as the number of cases caused by several infection clusters rises.

Up to 51 locally transmitted cases among the total 54 new cases reported between 3pm Thursday and 3pm on Friday were related to the recent clusters in Beijing, said Liu Xiaofeng, deputy director of the Beijing Center for Disease Prevention and Control, at a news conference on Friday.

"The Omicron variant spreads fast and it's hard to discover at the early stage due to the mild symptoms, which has added the difficulties to cut the transmission," he said. "Since the city government only adopted the control measures in severe areas of epidemic to ensure the normal economic operation, some hidden transmission across the districts occurred due to the flow of the residents."

The city will adjust the control and prevention measures based on the development of the epidemic, he said.

Beijing reported several clusters recently, including two involving a university and a wholesale market.

The latest cluster reported on Monday, involving a branch campus of Beijing Institute of Technology in Fangshan district, has led to 11 confirmed cases by Friday afternoon.

All of the 671 teachers, students and other staff members of BIT in this campus have been transferred to centralized quarantine places, said Li Zhenjian, vice-principal of BIT.

"The institute has sent more teachers and staff into the centralized quarantine location to take care of the students," he said. "We will make all efforts to ensure the students' health and safety."

Other disinfection work and control measures have been taken in the campus as well as the universities nearby. According to Fangshan district on Thursday, campuses of the other five universities near the area have been closed to outsiders under strict control measures.

Fengtai district, where the cluster involving a wholesale market occurred, has reported 24 COVID-19 cases and six asymptomatic infections between 3pm Thursday and 3pm on Friday.

Residents in Fengtai are asked to work from home and public transportations, including buses and subways in the districts suspended operation except for the bus stops and subway stations near the Beijing West Railway Station.

All restaurants in Beijing should continue to suspend dine-in service and schools continue to be closed to outsiders.