A bus in Pakistan caught fire after hitting a van parked on the hard shoulder of an intercity motorway in the eastern province of Punjab, killing at least 20 people and injuring 11 others, police and rescue officials said.

The accident occurred early Sunday near Pindi Bhattian, where the Islamabad-bound bus hit a van parked on the hard shoulder of the Lahore-Islamabad motorway, senior police officer Fahad Ahmed said.

The van was carrying fuel drums, which caused an inferno that engulfed the bus, Mr Ahmed said.

There were more than 40 passengers on the bus.

Those who were rescued were badly burned, including several in a critical condition. Other passengers were slightly injured with burns after escaping through the windows.

The drivers of both vehicles died, police said.

Mohammad Jawed, a medical officer at a hospital in nearby Faisalabad district, said two of the seriously burned injured died in the hospital, taking the death toll to 20.