Adjust font size: A medical worker collects sample to conduct nucleic acid test at a sampling site in Shunyi District of Beijing, capital of China, Dec. 28, 2020. [Photo/Xinhua] Beijing has expanded its nucleic acid testing and tightened COVID-19 prevention and control measures following new reports of local COVID-19 infections, local authorities said on Monday. The city faces a grim and complicated situation with risks of further infections still present, said Xu Hejian, a spokesperson for the Beijing municipal government, at a press briefing. Several locally transmitted cases have recently emerged in Chaoyang, Xicheng and Shunyi districts of Beijing, again sounding the alarm for COVID-19 prevention and control.