The second round of mass virus testing is underway in Horgos, a border city in northwest China's Xinjiang Uygur Autonomous Region, after the city found two asymptomatic COVID-19 cases, local authorities told a press briefing on Monday. 

The first round of testing has found no new positive cases after over 38,000 people were tested.

The source of the two positives remains unclear. An epidemiological investigation of the two asymptomatic cases is underway, local officials said.

The pair was from the same family. Neither of them have travel history to medium- or high-risk areas for COVID-19 in the past 14 days, or any contact with another positive or suspected COVID-19 cases.

Officials also said they had not touched cold chain products either.