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

The accident happened on a highway in rural Guizhou Province when the vehicle carrying a total of 47 people “tipped over on its side,” Sandu County Police said in a statement released on social media.

The other 20 people were being treated for injuries and emergency services were dispatched to the scene, police said, without giving further details.

The accident happened in Qiannan Prefecture – a poor, remote and mountainous part of Guizhou inhabited by several ethnic minorities.

Two social media posts by the China Road Network monitoring service, which have since been deleted, said the accident happened around 2:40 a.m. (1840 GMT on Saturday), according to screenshots posted on the Twitter-like Weibo were spread.

Social media users angrily questioned why a passenger bus was driving down a motorway in the early hours when many main roads in the province were closed to regular traffic.

“This feeling cannot be represented simply by lighting a candle and saying RIP,” reads a Weibo post that has more than 15,000 likes.

One hundred toll booths are closed in Guizhou due to Covid-19 restrictions, and long-distance passenger travel across China is banned between 2:00 a.m. and 5:00 a.m.

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

The provincial capital Guiyang, home to six million people, went into lockdown in early September.

According to police, the bus was headed south toward Guiyang in Libo County.

Unconfirmed photos shared widely on social media on Sunday showed a gold-colored passenger bus, its roof completely crumpled, being towed by a truck.

Another viral photo showed the bus traveling at night before crashing, with the driver and passengers wearing white hazmat suits, which are still commonly worn in China for protection against Covid-19. AFP could not verify the photos.

Traffic accidents remain fairly common in China, where erratic enforcement and lax safety standards have resulted in a string of fatalities over the years.

Guizhou has also seen other transportation accidents.

In June, a train driver was killed when a bullet train derailed in Guizhou province.

And in March, a Chinese passenger plane crashed, killing all 132 people on board, making it the deadliest plane crash in China in decades.