HARBIN, June 8 (Xinhua) -- Large-scale nucleic acid testing in the city of Mudanjiang, northeast China's Heilongjiang Province, has revealed 19 new asymptomatic carriers, local authorities said Monday.

The new cases came to light after tests were conducted on 658,772 people between June 1 and June 7, with the youngest case being a five-year-old child and the oldest aged 70, officials said at a press conference.

The city has been enhancing its efforts to screen for novel coronavirus infections, with 2,330 medics and more than 15,000 officials and community workers mobilized to collect samples.

The city's testing capacity reached 211,800 tests per day after it cooperated with other nucleic acid testing institutions in the province.

The tests were conducted free of charge for residents living in urban districts of the city, according to the municipal government.

As a border city in Heilongjiang, Mudanjiang still faces risks of both domestically-transmitted and imported cases of COVID-19.