BEIJING (AP) — A fire on a tour bus traveling along a highway in central China has left 26 people dead and as many as 30 injured, local authorities reported Saturday.

Five of those injured remained in critical condition, according to the Hunan province’s spokesman’s office.

The incident occurred at around 7:15 p.m. (1115 GMT) Friday along a stretch of Hanshou County in the city of Changde. Aboard were 56 people, including 53 passengers, a tour guide and two drivers, both of whom have been detained as authorities investigate the cause of the accident. Changde authorities put the number of injured at 30.

Photos from the scene show the 59-seater bus’s interior completely charred, possibly indicating the fire started with materials on board.

Industrial and transport safety remain major problems in China, with at least 62 people now reported dead in a massive chemical explosion Thursday in the eastern province of Jiangsu.

Previous deadly incidents aboard buses in China, including arson attacks, have been determined to have been caused by passengers or drivers bearing grudges against their employers or society.