(CNN) -- A bus caught fire in the southeastern Chinese city of Xiamen on Friday, killing at least 20 people at injuring more than 30 others, state-run news agency Xinhua reported, citing local officials.
The vehicle was on an elevated bus lane and more than a quarter-mile from a bus stop when the flames started, an official in the coastal city told Xinhua.
It wasn't clear what started the fire. Witnesses said they heard explosions 10 minutes after the fire started, according to Xinhua.
A picture of the bus, published on Xinhua's website, showed a badly charred interior. An injured passenger told Xinhua that she smelled gasoline while on the bus, and then saw a fellow passenger breaking a window in an attempt to get out.
The incident is under investigation, Xinhua reported.