At least 17 children have been killed when their school bus collided with a truck in Pakistan.

The children, aged between 10 and 16, had been travelling back from a quiz competition when the head-on crash occurred 300 kilometres north of Karachi.

Another three adults also died in the accident and a dozen of the wounded are being treated at a nearby hospital.

Local television showed footage of parents searching desperately for their children. Many of the injured remain in a critical condition.

Appeals for blood donations were made from the loudspeakers of mosques.

Though no cause for the crash has been established, a police officer on the scene said that “speeding and recklessness” were to blame.