Sixteen schoolchildren and a teacher burned to death in eastern Pakistan early yesterday when a short-circuit near a leaking fuel tank caused their minibus to burst into flames.
Police officer Ijaz Ahmad said five children were also injured, three of whom were in critical condition, in the blaze in Gujrat, 200km northwest of Islamabad.
The children were aged between six and 12.
Local police chief Dar Ali Khattak said the fire erupted in the vehicle when the children were only a few kilometres from their school.
Earlier, police had blamed an exploding natural gas cylinder for the incident. The bus was powered by both types of fuel.
TV footage showed the charred minibus and relatives of the victims crying at a hospital.
A schoolgirl told Pakistan's Geo news channel that the driver escaped when the vehicle went up in flames.
Authorities said they were trying to track him down and arrest him.
Ahmed said the driver could have saved many lives.
"We have been told that he fled from there when the children were crying for help," the police officer said.
President Asif Ali Zardari expressed "deep shock" over the incident and instructed medical personnel to provide the best care to the injured children.
Vehicles in Pakistan mostly run on both petrol and natural gas.
The country has one of the world's worst records for fatal traffic accidents, due to poor roads, badly maintained vehicles and reckless driving.
Additional reporting by Agence France-Presse