BEIJING, May 16 (Xinhua) -- In the first half of May, most of the domestically transmitted cases of COVID-19 on the Chinese mainland came from clustered infections, said a Chinese health official Saturday.

Asymptomatic cases were reported in various places across the country during the period, said Mi Feng, spokesperson for the National Health Commission, at a press conference.

In the first half of May, a total of 39 domestically transmitted cases and 194 asymptomatic cases were reported on the mainland, down 46 percent and 62 percent respectively from the second half of April, said Mi.

Mi stressed efforts to improve nucleic acid testing capabilities and step up screening, review, quarantine and management of asymptomatic cases.