A bus carrying private school pupils came off the road and fell into a ravine in Punjab province late Monday, killing at least 31 children and four adults.

"Thirty-five people, including 31 children and four adults, have been killed in the accident," said Naseem Sadiq, a senior administration official in the children's home district of Faisalabad.

"The driver, his helper, vice principal and a teacher of the school were among the dead... All the children were aged 10 to 15," said Dr. Sultan Alamgirian, head of Chakwal's main district hospital, where the dead and injured were rushed after recovery operations.

Authorities said investigation is underway, but early findings pointed to the failure of the brakes as reason for the accident.

ABC News reports, Pakistan has one of the world's worst records for deadly traffic accidents, blamed on poor roads, badly maintained vehicles and reckless driving.

In June, at least 12 children were killed and two others wounded when their school bus plunged into a canal in Pakistan-administered Kashmir.