State media say an express bus has burst into flames in eastern China, killing at least 20 people and injuring more than 30.

The official Xinhua News Agency says the fire occurred Friday during the evening rush hour in Xiamen city.

A local fire official who only gave his surname, Sun, said bodies were piled up inside the bus and a precise death toll was not immediately available. He said the cause of the fire is being investigated.

Xinhua said operation of the entire express bus system was suspended after the accident.

Pictures on Chinese social media showed huge clouds of black smoke rising from a burning bus on a highway.