Peshawar: At least 40 people, including women and children, were killed when a bus they were travelling in fell into a ravine in northwest Pakistan's Khyber Pakhtunkhwa on Friday, officials said.

The Peshawar-bound bus departed from Quetta in Pakistan's Balochistan province. The accident took place after it reached Dera Ismail Khan district in Pakistan's Khyber Pakhtunkhwa province, officials said.

A preliminary investigation suggests that the brakes of the bus failed, causing the driver to lose control while navigating a difficult bend on the mountainous terrain. The bus skidded off the road and fell into the ravine.

However, an investigation has been initiated to further examine the cause, officials said.

“According to initial reports, 40 people have been killed and eight others injured in the accident,” said Shahid Rind, media and political affairs adviser to Balochistan Chief Minister Sarfraz Bugti.

“District administrations from both provinces, rescue and other relevant departments are providing assistance to the affected persons,” he said.

According to the 1122 rescue service, there were 48 people on board when the incident happened.

The Dawn newspaper reported that 36 people were on the bus when it departed from Quetta, while the remaining passengers boarded along the route.

Deputy Commissioner of Sherani district Wali Khan Kakar said the identification of the deceased and the injured was underway.

Road accidents are common and often fatal in the mountainous regions of Pakistan's Khyber Pakhtunkhwa because of a combination of factors, including treacherous terrain, extreme weather, frequent traffic violations, poor road conditions, poorly maintained vehicles and untrained drivers.

Pakistan President Asif Ali Zardari directed the relevant authorities “to ensure the provision of all possible and best medical facilities to the injured”, his office said in a statement.

“The entire nation shares equally in the grief of the affected families in this tragic incident,” the statement added.