The interior minister of Sindh region, Abd al-Raauf Sidiqi, told Aljazeera just hours after the crash on Wednesday that 110 people were confirmed dead, another 15 bodies were believed to be still under the wreckage and that 107 had been seriously injured.
The accident occurred at about 4am when a train sitting in a station near Ghotki, in southern Sindh province, was hit by a second train, said Abdul Aziz, a senior controller at Pakistan Railways.
The collision caused several carriages to derail and spill over onto another track, where they were struck by the third train, causing further derailment, he said.
"It is a very gruesome situation," local police official Aga Mohammed Tahir said.
"Rescue workers have started to pull the dead and injured out. There were many people inside and there are a lot of casualties."
Tahir said that dozens of people had been killed or injured, but that no exact figures would be possible for some time. He said at least 13 train carriages derailed, and that the injured were being taken in ambulances and cars to area hospitals.
"They are being pulled out every minute," he said. Abdul Aziz also said he expected the toll of dead and injured to be high. "We fear that there could be many casualties," he said.
"Rescue workers have started to pull the dead and injured out. There were many people inside and there are a lot of casualties"
Aga Mohammed Tahir,
Ghotki is about 600km northeast of Karachi, in a remote area. Abdul Aziz said rescue teams had been dispatched, but that it could take some time for them to reach the site in force.
A second railway official, Sajjad Ahmed, said the train in the station was the Quetta Express, which was bringing passengers from the eastern city of Lahore to the southwestern city of Quetta when it developed a technical problem.
Technicians were working on the train when it was hit by the Karachi Express, a night-coach passenger train from Lahore to the southern port city of Karachi.
The impact pushed three carriages onto an adjacent track, and they in turn were hit by the oncoming Tezgam Express, which was bringing people from Karachi north to Rawalpindi, near the capital.
Pakistan's railways are antiquated, and dozens of people have been killed in train accidents in recent years. On 5 March, five people were killed and 25 injured when a passenger train derailed in eastern Punjab province.
And on 20 September 2003, a train ploughed into a packed bus in central Pakistan, killing at least 27 people and injuring six others.
Accidents are often blamed on faulty equipment or human error.