North China's Tianjin Municipality has started citywide nucleic acid testing after 20 people tested positive for COVID-19, authorities said on Sunday. Gene sequencing found the first two locally transmitted confirmed cases were infected with the VOC/Omicron variant, the municipal headquarters for COVID-19 prevention and control said. 

The citywide testing was expected to be completed in 24 hours, from 7 a.m. Sunday in four districts, and from 7 a.m. Monday in 12 other districts. Tianjin has a population of about 14 million, according to national census data released in May.