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

The death toll from a bus blaze on Friday in the city of Chengdu, capital of southwest China's Sichuan Province, has risen to 25, government authorities said.

Among the 76 injured, six were in critical condition, said Mao Zhixiong, spokesman for the Chengdu city government Friday afternoon at a news conference.

All the injured were sent to the Chengdu No.2 People's Hospital and the Chengdu Army General Hospital.

The fire began at 8:02 a.m. when the No.9 bus, with license plate Chuan A 49567, was on its way from Tianhui Township to downtown Chengdu, and caught fire under the Chuanshan Viaduct, said Mao.

Sichuan's Communist Party chief Liu Qibao and provincial governor Jiang Jufeng both ordered "all-out efforts to treat the injured".

"The bus had air conditioning and only the windows at the rearmost seats could be opened by hand," said 29-year-old Deng Huaqiong. She sat on the second row from the rear and jumped out after someone opened the back window. She suffered slight burns and was receiving treatment in hospital.

Tao Shouliang, another survivor, said he was standing behind the driver when he saw thick smoke filling the bus.

After passers-by smashed the windows from the outside, he first threw his granddaughter out and then jumped out of the bus, with some of his hair burnt, Tao told Xinhua.

But his wife failed to escape immediately and was injured. She is being treated in hospital.

"There was a strange smell in the bus when it was on Chuanshan Viaduct, but the driver refused to stop and said the smell should be dealt with after the bus was off the viaduct," said a relative of a wounded passenger.

"In a few seconds, the fire broke out," said the relative.

A female motorist surnamed Li said she saw the smoke emerging from the back and pulled alongside the bus to warn the driver. She blew her horn and made gestures, but he ignored her. The fire started a few kilometers along the road.

A witness said he saw thick smoke and some passengers flee from the burning bus, their clothes and skin burnt, and bleeding, while some passers-by were searching for extinguishers.

"The driver escaped the fire and helped in the rescue," said a vendor near the bus station. More than 10 people escaped from the bus.