At least 40 people were killed and eight others injured after an overcrowded passenger bus plunged into a rocky ravine in Pakistan's southwestern Balochistan province early Friday, officials said.

The accident occurred in the Dana Sar area, near the border between Balochistan and Khyber Pakhtunkhwa provinces, when the speeding bus went out of control and fell into a deep ravine, according to Shahid Rind, spokesperson for the Balochistan government.

Rind said the bus was carrying more passengers than its capacity after taking aboard people from another bus that had broken down along the route.

Rescue teams reached the scene and began efforts to identify those killed in the crash.

President Asif Ali Zardari expressed deep sorrow over the tragedy, offering condolences to the families of the victims and wishing the injured a speedy recovery. He also directed the relevant authorities to ensure the injured receive the best possible medical care.

Balochistan Chief Minister Sarfraz Bugti also expressed grief over the loss of lives and instructed officials to provide the best available treatment to those injured.

Road accidents are frequent in Pakistan due to poor road conditions, weak enforcement of traffic regulations and unsafe driving, especially on mountainous roads.

In May, 17 people were killed and five others injured when a minibus crashed into a bus parked along a motorway in northwestern Pakistan.