A large bus carrying 56 people burst into flames at around 10:20 a.m. local time (0220 UTC) on Sunday after crashing into a barrier along a highway in central China.

At least 30 people died and 21 others were injured in the crash and ensuing blaze, Xinhua news agency reported, adding that the driver of the bus had been detained for questioning.

Video footage posted online by the state broadcaster showed thick black smoke billowing from the vehicle, as passengers looked on from nearby.

The cause of the crash remained unclear. Xinhua said, however, that local officials believed an oil leak caused by the crash may have sparked the fire.

Traffic accidents are common in China. The World Health Organization estimates that more than 250,000 people die each year on the country`s roads.

Long-distance buses are popular in the country as a cheap way of traveling between cities, and competition between bus firms can be fierce.