A bus blaze has left 25 dead on Friday morning in the city of Chengdu, capital of southwest China's Sichuan Province.

The bus was always very crowded in rush hour and most of the emergency hammers to smash the windows on the bus had disappeared long ago, said people at the scene.

Fire fighters arrived at 8:09 a.m. and the fire was extinguished at 8:11 a.m., said He Jiansheng, deputy director of the Chengdu Public Security Bureau.

He said police were questioning the bus driver.

"The bus was not new and the temperature in Chengdu is not high," said a police officer with the bureau.

Traffic police told Xinhua that it was unclear how the fire started, and they are waiting for further technical investigations.

The shell of the burnt bus was towed away from the scene, which is only a few meters from the bus station. Traffic returned to normal around midday.

The bus was diesel-powered and made in February 2005. It had 270,000 km on the odometer.

An investigation team, led by Sichuan Vice Governor Li Chenyun, and including officials from the Sichuan government, the Public Security Ministry and the State Work Safety Administration, has been set up.

The dead were being identified, said Chengdu city government spokesman Mao Zhixiong.

Hu Guangwei,a researcher with Sichuan Academy of Social Sciences, said the tragedy revealed management problems in the urban bus sector.