At least 36 people died when a double-decker sleeper bus slammed into the rear of a methanol tanker and burst into flames on Sunday in China's worst traffic accident in more than a year.
Both vehicles caught fire and only three of the 39 people onboard the bus survived the motorway crash, which occurred in the early hours of the morning in Shaanxi province, the state Xinhua news agency said.
A traffic police official said the fact most the passengers were asleep at the time might account for the high number of deaths, while there were also suggestions they had been unable to escape because there was only one door.
A total of 36 bodies were pulled from the charred shell of the bus and three people were taken to hospital. The driver and passenger of the tanker were taken into police custody, Xinhua said.
It appears the bus slammed into the back of the tanker as it was re-entering the motorway from a service station in the northern Yanan City, according to a report on the website of the Shaanxi government.
Skid marks stretching for ten metres (32 feet) were clearly visible on the road, suggesting the bus had noticed the tanker in its path before the collision, the report said.
"Only the shell remains, it is not possible to see even the luggage or the passenger seats in the wreckage," the Shaanxi website said, quoting a report from state-run China Central Television (CCTV).
"The bus also only has one door, which could be a reason that the passengers could not escape."
Pictures showed the front of the tanker was unscathed, while the bus had been almost completely destroyed by the blaze.
The accident was the worst in China since a fire on an overcrowded sleeper bus carrying flammable materials killed 41 passengers in central China in July last year, according to the country's work safety watchdog.
Yue Jiuxiang, a local traffic police official in charge of the rescue operation, told CCTV: "Soon after the collision, the bus was engulfed by flames.
"The front part of the bus was seriously damaged. Most of the passengers were sleeping. This is why so many people died."
Police were investigating the cause of the accident, which happened on the Baotou-Maoming Expressway, which spans the length of China from the northern city of Baotou to the southern province of Guangdong.
The bus -- which was not overcrowded -- had departed Hohhot in Inner Mongolia at 5:00 pm on Saturday and was heading to the Shaanxi provincial capital Xian when the collision occurred, reports said.
An official at Yanan city government information department surnamed Liu confirmed the death toll.
Separately, ten people were killed and two injured when a van and a truck collided in southwest China, Xinhua said, without providing more immediate details.
China's roads are highly dangerous, with traffic laws and safety widely flouted, and truck drivers typically overworked.
Last year, more than 62,000 people died in traffic accidents, state media said, citing police figures.
Vehicles carrying explosive materials -- which must first get permission from the police before travelling on the roads in China -- are involved in many accidents.
Buses are also commonly involved in road accidents as operators often seek to cram as many people as they can into their vehicles to maximise profits and drivers hurtle down highways.
The July 2011 accident involved a double-decker which was reportedly only designed to carry 35 passengers but had 47 people on board.
It was taking people to southern Hunan province when it caught fire in the early morning.
Twenty-three people were killed and three injured in April when a bus and truck collided in the eastern province of Anhui.
Another collision between a tour bus and a truck the same month left 13 dead and 21 injured.