Fifty-one people are believed to have killed in a fiery bus crash in China's mountainous southwest. 

China's official Xinhua news agency reported the bus left the road and plunged 100 meters into a valley in Sichuan province.  Witnesses say they heard an explosion and saw black smoke rising from the crash site.

Xinhua says Sichuan's provincial governor, Jiang Jufeng, was on his way to supervise rescue and recovery efforts.  There are no reports of any survivors.

The bus was on its way from Sichuan to Ningbo, a coastal city south of Shanghai in eastern Zhejiang province

China's roads are among the most dangerous in the world with accidents often caused by reckless driving, poor road conditions and overloaded vehicles.

Some information for this report provided by AFP, AP and Reuters.