An explosion on a bus killed 11 people and left three critically injured in Tianzhu County in Southwest China's Guizhou Province yesterday.

An expert team is still investigating whether the blast was caused by a bomb, a local government spokesman told China Daily.

"The explosion could be heard 400-500 metres away, but it's too early to say if it was a bomb," an official with the county government's press office said in a telephone interview.

"A team of experts from the provincial government are still determining the cause."

He would not say whether the blast was an accident or a deliberate act.

The blast occurred at 7:05 am in Tianzhu town, the administrative centre of Tianzhu County. The official said six people were killed on the spot and another five died in hospital.

He didn't reveal whether the dead and injured were passengers or passers-by, or how many people were on the bus.

"Nearly all government staff rushed to the site after the blast and I was the only one left behind on duty," said the official, who refused to be named.

A hospital source said 15 injured people are still being treated at Tianzhu People's Hospital.

"Three are still in a critical condition, but the lives of the other 12, who have minor injuries, are not in any danger," said the hospital's administration officer, surnamed Wang.

Wang said her hospital is monitoring the injured around the clock.

Source: China Daily