Fifteen people are dead after a bus overturned into a ravine in southwest China, state media said.

Xinhua, the official news agency, said the bus was carrying 21 people along a mountain road when it flipped and "plunged into a deep valley" today at around noon.

Another six people were injured in the accident, which happened in Aba prefecture (called Ngawa in Tibetan), a mountainous area of China's Sichuan province that has a large Tibetan population.

The ethnicity of the victims was not reported, and the cause of the accident is still under investigation, Xinhua said. 

The bus was traveling from Chengdu, the provincial capital, to Ma'erkang (Barkam) in Aba prefecture. 

More from GlobalPost: Tibetan mother of 4 self-immolates to protest Chinese oppression (VIDEO)

More from GlobalPost: Chinese cars, made in Bulgaria