China reported the highest number of asymptomatic COVID-19 cases in nearly seven months, following a mass infection of an unknown origin in the northwestern Xinjiang region. (Photo: Reuters)

Xinjiang health authorities found 137 asymptomatic cases on Sunday amid a testing drive for the more than 4.7 million people in the Kashgar area triggered by an asymptomatic infection in a 17-year-old female garment factory worker reported on Saturday.

It was not clear how she was infected, though all of the new cases were linked to the garment factory.

The woman’s case was discovered during routine testing but it was not clear why she was subject to such testing, Chinese media reported quoting health officials.