BEIJING — Authorities have ordered mass coronavirus testing and locked down some locations in the southwestern Chinese city of Chengdu following the detection of two new virus cases there.

Chengdu health officials identified the cases as a 69-year-old woman, who’s condition is listed as serious, and her 71-year-old husband who has yet to show symptoms.

Officials at a Monday night news conference said they are still investigating the source of the infection in Sichuan province’s capital and largest city that has been relatively unscathed by the pandemic. However, samples taken at the couple’s apartment showed the presence of the virus in seven different locations, including on door knobs, light switches and food in the refrigerator, indicating a “high degree of contamination,” Zhu Xiaoping, head of the provincial coronavirus task force was quoted as saying.

Five locations in Chengdu’s Ludu district have been sealed off, including a hospital, a school and a wholesale market and more than 21,000 people tested as of Monday evening, the government said.

China reported a total of 12 new cases on Tuesday, including the two in Chengdu and 10 brought from outside the country, bringing China’s total to 86,646 with 4,634 deaths.