Medical staff of Xiaotangshan Hospital clean up a ward after the hospital cleared all COVID-19 cases in Beijing, capital of China, April 28, 2020. [Xinhua/Peng Ziyang]

BEIJING -- Over the past 10 days, the number of asymptomatic COVID-19 cases still under medical observation dropped by 22 percent on the Chinese mainland, a health official said May 14.

No more than 20 new asymptomatic cases have been reported each day over the period, said Song Shuli, a spokesperson for the National Health Commission, at a press conference in Beijing.

However, the official warned that close contacts of domestically transmitted cases are still increasing, requiring greater efforts in testing and screening to identify the infection sources and the scope of the virus spread as soon as possible so as to forestall any resurgence of infections.