At least 63 people have been killed after two express trains collided in southern Pakistan on Monday morning.
More than 100 passengers were also injured, authorities said, as rescuers and villagers worked to pull injured people and more bodies from the wreckage.
The accident occurred when the Millat Express derailed at around 03:30 and was hit minutes later by the Sir Syed Express. It was not immediately clear what caused the derailment and the subsequent collision.
Pakistani Prime Minister Imran Khan said on Twitter that he was "shocked by the horrific train accident" and that he had asked the railway minister to supervise the rescue work and also ordered a "comprehensive" probe into the crash.
Officials in Sindh province confirmed on Tuesday that the death toll had risen to 63 passengers.
According to railway authorities, about 1,100 passengers were on board the two trains, and arrangements were being made to help the surviving passengers.
Footage from the scene showed ambulances transporting the injured to hospitals. Some of the wounded passengers were listed in critical condition.
Heavy machinery was used to cut open some cars, in the hopes of rescuing several people who were still trapped in the wreckage, hours after the collision.
Officials at Pakistan railways said they had ordered an investigation and rescue work was still in progress.
Earlier, Azam Swati, the minister for railways told the Associated Press that engineers and experts were trying to determine what caused the collision and that all aspects would be examined, including the possibility of sabotage.
Habibur Rehman Gilani, chairman of Pakistan Railways, told Pakistan’s Geo News TV that the segment of the railway tracks where the crash took place was old and needed replacing, without giving further details.
Aijaz Ahmed, identified as the driver of the Sir Syed Express, also 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.
Mohammad Amin, one of the passengers on the Millat Express who had minor injuries, told the AP from a hospital that before the train departed from the southern port city of Karachi, he and his brother, who was also on the train, saw railway mechanics working one of the coaches.
That led them to believe there was something wrong with it but they were reassured all was fine. The train car that was being worked on was the one that later derailed, Amin claimed.
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 ploughed into a standing freight train in southern Pakistan, killing 210 people in the worst rail disaster in Pakistan’s history.