The victims of a bus crash which killed 27 people and injured a further 20 in southwest China's Guizhou province were in an official government health vehicle and were being transported for Covid reasons, local media reported.

The accident took place in the early hours of Sunday morning on a highway in Sandu county, which lies around 170km southeast of the provincial capital, Guiyang, police said.

The bus, which overturned on a section of a highway that leads from Guiyang to Libo, a county just south of Sandu, was carrying 47 people, the police statement added. All 20 injured were being treated in hospital on Sunday, an official from Sandu county government's publicity department said.

"At present, on-site rescue work is basically completed, the treatment of the injured and aftercare of the deceased are being carried out in an orderly manner, and the cause of the accident is under investigation," the local government said in a social media statement.

Guiyang and the wider Guizhou province have seen a rise in Covid cases in recent days.

Local media Caixin reported that the victims were being transported for Covid reasons, citing sources at the Sandu County Emergency Management Bureau. Soon after, a report in Tianyan News, which belongs to the state-owned Guizhou Daily, said the bus was a vehicle specifically designed for transporting people to and from Covid quarantine.

On Saturday, Guizhou's authorities announced on their official WeChat account that those needing to be quarantined would "need to be transported to sister cities and states" due to limited capacity in Guiyang. (Agencies)