People register before entering the 9.18 Historical Museum in Shenyang, capital of northeast China's Liaoning Province, March 17, 2020. [Xinhua/Long Lei]

SHENYANG -- More than 7,500 people in the northeastern Chinese city of Shenyang have been put under medical observation and are undergoing nucleic acid testing for COVID-19, the municipal government said May 14.

The measure came as local authorities have strengthened their response to the coronavirus epidemic after the city recently reported three confirmed cases.

One case, which was reported on May 10, is believed to have ties with the confirmed cases in Shulan, a city in Jilin Province, said Sun Baijun, director of the Center for Disease Control and Prevention in Shenyang, adding that two of the patient's co-workers were later confirmed to have been infected with the virus.

Out of the 7,500 people under medical observation, 1,093 are close or indirect contacts of the three confirmed cases.

Authorities in the northeastern city of Jilin, which administered Shulan, have adopted several extra stringent measures to curb the spread of the COVID-19 epidemic.

The measures include suspending all coach and tourist charter bus services and applying closed-off management to all the city's residential communities and villages.