BEIJING, May 18 (Xinhua) -- Beijing reported 49 new locally transmitted COVID-19 infections between 3 p.m. Tuesday and 3 p.m. Wednesday, Liu Xiaofeng, deputy head of the Beijing municipal disease prevention and control center, told a press briefing on Wednesday.

Forty-five cases were detected among people under closed-off management and four were found through mass screening in communities, Liu said.

Infections were detected on a campus of the Beijing Institute of Technology in Yancun Township, Fangshan District. All of the 670 teachers and students on the campus are being transferred to a centralized quarantine site, Zhang Mingzhi, an official with the district, said at the press briefing.

From Thursday, commuters between Beijing and neighboring Tianjin Municipality will be required to show negative nucleic acid test results no older than 48 hours if they enter or leave the national capital.

Previous rounds of mass screening in Beijing detected sporadic hidden infections in a timely manner, which played an important role in cutting off the spread of the epidemic, said Wang Xiao'e, an official with the Beijing municipal health commission.

"For the next step, our screening will mainly focus on key areas, sectors and groups," Wang said.

Starting Thursday, Beijing will conduct three days of mass nucleic acid testing in the four districts of Xicheng, Haidian, Fengtai and Fangshan as well as subdistricts in other areas where COVID-19 infections were reported over the past seven days.

The national capital has classified 15 areas as high-risk for COVID-19 and 32 as medium-risk.