Three people have been killed and up to 40 injured in a Pakistani train derailment, officials say.

Initial reports suggest that six coaches derailed and plunged down an embankment near Jhelum city in eastern Punjab province.

Officials say there could be about 400 passengers in the carriages and they fear the casualty numbers will rise.

The high-speed train was travelling to the city of Lahore from Rawalpindi.

Troops have been sent to join rescue operations, while ambulances headed to the area, which is inaccessible by road.

Rescuers worked in darkness with whatever equipment was available to pull out the survivors.

One survivor quoted by the Associated Press said he was riding in the first carriage when he heard a big bang and felt a huge jolt.

"I heard screams," Javed Butt said.

The railway authorities say they will launch an inquiry after the rescue effort is complete.

Hundreds of people have died in recent years on Pakistan's railway.

More than 130 people were killed near the southern town of Ghotki last July, in Pakistan's worst train disaster in at least a decade.

Correspondents says casualty figures are often so high because trains are packed with far greater numbers than they were designed for.

PHOTO CAPTION

A Pakistani passenger crosses a rail-track with luggage to catch a train at the railway station, in Karachi in 2005. (AFP)