At least 40 people were killed in Pakistan after a speeding passenger bus crashed into the pillar of a bridge and fell into a ravine in the remote Balochistan province on Sunday, a senior official said.

The vehicle with at least 48 passengers on board was travelling from provincial capital Quetta to Karachi, the capital and main city of Sindh province when it crashed into the pillar and subsequently careened into a ravine before catching fire.

The accident took place in the Lasbela area due to speeding, Hamza Anjum, Assistant Commissioner Lasbela, told the media.

"The bus crashed into the pillar of a bridge while taking a U-turn near Lasbela and fell into a ravine and then caught fire," he said.

Only three people, including a child and a woman, could be rescued alive, the official said, adding that the death toll could rise.

Police and rescue officials were busy in pulling out bodies and shifting them to the nearby hospitals, according to officials.

Road accidents are common in Pakistan and most of them are caused due to careless driving and bad road conditions.