A crowded passenger train has derailed in southern Pakistan killing at least 56 people and injuring more than 120.
The scene of the crash was strewn with the wrecked carriages
More than 12 carriages of the overnight train travelling between Karachi and Lahore came off the rails near the city of Mehrabpur in Sindh province.
Some carriages plunged into water. The express train was packed with passengers returning home for the Islamic festival of Eid al-Adha.
Officials say the likely cause for the crash was a faulty track.
Hundreds of people have died in recent years in accidents on Pakistan's railways.
The crash happened shortly after 0200 on Wednesday (2100 GMT on Tuesday) in a remote area, about 400km (250 miles) north of Karachi.
"We were almost asleep when we heard something - a big bang," passenger Shahid Khan told Reuters news agency.
"Then I felt I was flying through the air and the carriage was tumbling to the ground.
"We were grappling in the darkness. Somehow we managed to make it out."
Some carriages were severely damaged and others came to rest in water near the track after the train slid off the embankment.
The scene of the crash was strewn with twisted metal and passengers' personal belongings.
Rescue workers struggled with large numbers of casualties - including children - in the dark and cold and did not have equipment to cut open the carriages, officials said.
Many local people turned out to help, carrying the injured away on rickshaws, motor-scooters and donkey carts.
Col Maqsood Ali, who was at the site of the crash, told the BBC that up to 50 people were seriously injured, and that the number of dead was likely to rise further.
Officials said the most likely cause of the crash was the track which cracked in the cold weather.
"There's a joint in the track which is welded and that has broken. It shrinks in winter," Asad Saeed, the general manager of Pakistan's railways, told Reuters.
Mr Saeed ruled out sabotage.
Hours after the accident, rescuers were still trying to cut into at least one of the carriages. Trapped passengers were heard calling for help.
Local officer Ghulam Qadir told the AFP news agency: "People are trapped in the wreckage and there are cries for help. Policemen pulling out the dead and injured... drenched in blood."
Khalid Amin, a senior railway official, said two relief trains had been dispatched to pick up survivors.
Pakistan has a history of deadly accidents on its ageing railway system.
Signalling faults and poorly maintained tracks are often the cause of the accidents.
Correspondents say casualty figures are often so high because trains are packed with far greater numbers than they were designed for.
More than 130 people were killed when three trains collided in Sindh province in July 2005 in the country's worst train disaster for 15 years.