A tour bus plunged into a Tibetan valley on Saturday after hitting two vehicles, killing 44 people and injuring 11, China's official news agency Xinhua reported.

"The 55-seat bus carrying 50 people fell off a 10-metre-plus-high cliff after crashing into a sports utility vehicle and a pick-up truck," the report said, citing the regional government.

Another five people were in the other vehicles in the accident which happened at around 4:25 pm (0825 GMT) in Nyemo County, west of the capital Lhasa, in the Tibet Autonomous Region which is governed by China.

The bus passengers were mainly tourists from several eastern regions in China. The injured were being treated at hospitals in Lhasa and did not have life-threatening injuries, Xinhua said.

Pictures on the news agency's website showed rescue workers at the bus which was lying with its wheels in the air. A hoist was also pictured attached to the bus.

Police have detained the managers of a travel agency and vehicle tour company, blamed for the crash.

"The regional government has held an emergency meeting, ordering a general overhaul of road safety and travel safety across the region to avoid similar fatal accidents," the report added.

Fatal road accidents are a serious problem in China, particularly involving the country's often over-crowded long-distance buses.

The ministry of transport says the number of road deaths in China fell from 104,000 in 2003 to 60,000 in 2012, or from about 300 fatalities a day to less than 200.

A study published in 2011 by a group of Chinese and US researchers concluded, however, that the number of deadly accidents was twice higher than the police claimed.

In July, 43 people died when a van carrying inflammable liquid hit a bus on a motorway in central China.

In August 2012, at least 36 people died when a double-decker sleeper bus slammed into the rear of a methanol tanker and burst into flames in northern China.