The fatal accident occurred as people were returning to the port city of Karachi from Peshawar after celebrating Eid al-Adha.
At least four people were killed and more than 120 injured when two trains collided in central Pakistan early on Thursday, state-run Radio Pakistan has reported on its website.
The accident occurred when the Karachi-bound "Awam Express" passenger train rammed into a cargo train that had stopped after running over a man near Buch railway station in the Sher Shah town of Punjab Province's Multan District.
Rescue workers used metal-cutting equipment to try to reach injured passengers still trapped in the mangled wreckage.
A three-day public holiday for the festival of Eid al-Adha ended on Wednesday, and many Pakistanis are returning from their family homes to the cities where they work.
Mohammad Javed, 35, a shopkeeper who lives near the site of the pre-dawn crash, said he had been woken up by "a huge blast."
"I thought that some bomb had exploded," he told Agence France Presse.
"I came out of my house and saw a passenger train had piled up on a goods train. I heard people crying in pain and many lying outside the train.
"Survivors and locals were pulling out wounded people who were stuck in the wreckage."
Local state-run Rescue 1122 service spokesman Abdul Jabbar told AFP that more than 100 people had been hurt in the crash.
"The last trapped victim has been extricated after four hours by cutting thick metal sheets of train cartridge with the help of hydraulic cutters," a report by the Rescue 1122 service said.
The report also confirmed that four people had been killed
Munir Chishti, in charge of railway police, ruled out the possibility of sabotage, saying it was an accident.
Railway official Saima Bashir blamed the accident on the driver of the passenger train, saying he failed to heed a red signal that went up after the goods train had stopped.
Cranes and ambulances filled the area as troops also raced to the scene to help.
Major General Mohammad Arif said that the military would extend the best possible support to civil authorities to restore normal rail traffic and transferred the injured to hospitals.
Rescue official Khalid Hussain said 28 people had been taken to hospital, while scores more were treated on the spot.
Other media reports put the death toll at six with more than 150 injured.
Train accidents are common in Pakistan, which inherited thousands of kilometres of track and trains from former colonial power, Britain.
The railways have seen decades of decline due to corruption, mismanagement and lack of investment.
Last November, 14 people were killed and more than 100 injured in southwestern Balochistan Province after a train's brakes failed and it sped down the side of a mountain.
In July 2015, at least 19 people, including four army officers, were killed when a special train carrying military personnel fell into a canal after a bridge partially collapsed.
About 130 people were killed in July 2005 when a train rammed into another at a station in southern Sindh Province, and a third train hit the wreckage.