A bus crash killed 27 people in southwest China on Sunday, police said, the country’s deadliest road accident so far this year.

The accident took place on a highway in rural Guizhou province when the vehicle carrying a total of 47 people “flipped onto its side”, Sandu county police said in a statement published on social media.

The other 20 people were being treated for injuries and emergency responders were dispatched to the scene, police said, without providing any more details.

The accident happened in Qiannan prefecture — a poor, remote and mountainous part of Guizhou, home to several ethnic minorities.

Two social media posts by the China Road Network monitoring service, which have since been deleted, said the accident occurred at around 2:40am (1840 GMT on Saturday), according to screenshots circulating on the Twitter-like Weibo.

Social media users angrily demanded why a passenger bus was travelling down a highway in the early hours of the day when many major roads in the province have been closed to regular traffic.

“This feeling can’t simply be represented by lighting a candle and saying RIP,” read one Weibo post with more than 15,000 likes.

One hundred toll stations are shuttered in Guizhou because of Covid-19 restrictions and long-distance passenger journeys across China are banned from running between 2am and 5am.

Guizhou is in the midst of a Covid outbreak that has seen more than 900 new infections in the past two days alone.

Its provincial capital Guiyang, home to six million residents, was locked down earlier in September.

The bus was travelling south in the direction of Guiyang to Libo county, according to the police statement.

Unverified photos circulating widely on social media Sunday showed a gold-coloured passenger bus, whose top is completely crumpled, being towed by a truck.

Another viral photo appeared to show the bus driving at night before it crashed, with the driver and passengers wearing white hazmat suits, which are still commonly worn in China to protect against Covid-19. AFP could not verify the photos.

Road accidents remain fairly common in China, where irregular enforcement and lax safety standards have resulted in a string of fatalities over the years.Guizhou has also seen other transport accidents.

In June, a railway driver was killed when a high-speed train derailed in Guizhou province.

And in March a Chinese passenger jet crash killed all 132 people on board, marking the deadliest aviation accident to take place in China for decades.