A bus reportedly taking 47 people to COVID-19 quarantine in southwest China crashed before dawn Sunday morning, killing 27 and injuring 20 others, media said.

The bus overturned on an expressway in Guizhou province, a brief statement from the Sandu county police said, without mentioning any connection to quarantine. The injured were being treated, it said.

Chinese business news outlet Caixin said Sandu officials confirmed the passengers were "epidemic-related people" being taken from Guiyang, the provincial capital, to Lido county, which is about 200 kilometers (125 miles) southeast.

Guiyang reported about 180 new cases on Friday. China has maintained a strict "zero-COVID" policy that isolates infected people and close contacts to try to contain the spread of the disease.

The bus overturned about 2:40 a.m., according to an online report by an arm of the Guizhou Daily media group. Following the accident, it said that provincial leaders called for an examination into the pandemic transfer and isolation procedures.