The bus was returning from a school trip to a salt mine popular with tourists when it went into a ravine. Forty other people on the bus were injured.
The incident happened in Kalar Kahar, east of the capital Islamabad.
Pakistan has one of the world’s worst records for fatal traffic crashes, blamed on poor roads, badly maintained vehicles and reckless driving.
Speaking from the scene in Chakwal district, Punjab province, about 100 kilometres southeast of the capital, senior police officer Chaudhry Salim said at least 30 people were killed, including 24 school students.
He said the cause of the accident, which also left more than 55 injured, was brake failure.
"We have received 24 dead bodies and six to eight dead bodies were sent to another nearby hospital," he said.
Another official from the traffic police confirmed the accident and said 26 people, including 22 students, were killed on the spot.
He said the driver, his helper and the vice principal of the school were among the dead.
A government official said an inquiry had been ordered and an investigation team will examine the scene of the accident on Tuesday to examine the cause.
Pakistan has one of the world's worst records for deadly traffic accidents, blamed on poor roads, badly maintained vehicles and reckless driving.
source: theprovince.com, irishtimes.com
