At least 40 dead in Pakistan train crash

An express train has barrelled into another that had derailed in Pakistan, killing at least 40 people.

More than 100 were injured, and rescuers and villagers worked throughout the day to pull survivors and the dead from the crumpled cars.

Cries for help pierced the pre-dawn on Monday as passengers climbed out of overturned or crushed rail cars, and locals rushed to the scene in the district of Ghotki, in the southern province of Sindh.

Later in the day, heavy machinery arrived to cut open some cars, in the hopes of rescuing several people still believed to be trapped. The military deployed troops and helicopters to assist.

At around 3.30am local time the Millat Express train derailed and the Sir Syed Express train hit it minutes later, deputy commissioner of Ghotki Usman Abdullah said.

It wasn't immediately clear what caused the derailment, and the driver of the second train said he braked when he saw the disabled train but didn't have time to avoid the collision.

"The challenge for us is to quickly rescue those passengers who are still trapped in the wreckage," local police chief Umar Tufail said.

The death toll steadily rose through the day, reaching at least 40, according to Abdullah.

Officials said more than 100 passengers were injured, and those with critical injuries would be brought by helicopter to a nearby city's hospital.

According to railway officials, about 1100 passengers were on board the two trains.

Earlier railways minister Azam Swati said engineers and experts were trying to determine what caused the collision and that all aspects would be examined, including the possibility of sabotage.

Pakistan Railways chairman Habibur Rehman Gilani told Pakistan's Geo News TV that the segment of the railway tracks where the crash took place was old and needed replacing. He did not elaborate.

Aijaz Ahmed, the driver of the Sir Syed Express, told the station that on seeing the derailed train, he tried his best to avoid the crash by braking but failed.

Railway officials said Ahmed was slightly injured, and villagers pulled him from the train's engine after the crash.

Pakistani Prime Minister Imran Khan expressed his deep sorrow over the tragedy, saying on Twitter that he had asked the railway minister to supervise the rescue work and also ordered a probe into the crash.

According to local media, some of the passengers on the Millat Express were heading to a wedding party.

Train accidents are common in Pakistan, where successive governments have paid little attention to improving the poorly maintained signal system and ageing tracks.

In 1990, a packed passenger train ploughed into a standing freight train in southern Pakistan, killing 210 people in the worst rail disaster in the country's history.