At least 17 Pakistani school children are dead after a gas cylinder on their school bus exploded.

Local media say ten other children were injured. Most of the children were age 8 or younger.

It happened about 100 miles southeast of Islamabad.

A police officer said the fire started when the bus driver shifted from petrol to natural gas.

Many vehicles in energy-starved Pakistan are powered by relatively cheap compressed natural gas and cylinder blasts are common.