Authorities investigating a bus fire that killed 41 people have blamed the accident on hazardous chemicals that a passenger brought on the vehicle.

The accident occurred as the bus traveled on the Beijing-Zhuhai Expressway on July 22.

A report released by the State Council said the fire started when 300 kilograms of azobisisoheptonitrile stored in 15 boxes overheated.

The chemical, which is highly flammable and should be carried in a refrigerated unit, burst into flames at about 4 am as the bus reached Xinyang in Central China's Henan province, either from friction or heat from the engine, the report said.

The 35-seat bus was carrying 47 passengers. Only six survived the accident, which caused a direct economic loss of 23.42 million yuan ($3.68 million).

The report added that 32 people are facing Party or administrative disciplinary action, while 10 others have been detained on charges relating to the accident.