At least 20 people have been killed after a train collided with stationary coaches in Pakistan, hospital officials have said.

Television footage showed mangled and overturned carriages at the scene at the railway station in Karachi, Pakistan’s biggest city, as rescue workers tried to free people still trapped inside the wreckage.

A further 65 people are said to have been injured and a senior administration official said there could have been up to 1,000 people on board at the time of the crash.

Rescuers armed with metal cutting equipment and heavy cranes were joined by the military and the police.

The engine of one train appeared to have been completely destroyed but the full extent of the damage is unclear.

Khwaja Saad Rafique, Pakistan’s railways minister, said the collision occurred between a moving Zakaria Express and a stationary Fareed Express and they were looking at negligence as a possible cause as a stop signal appeared to have been ignored.

He said the whereabouts of the driver of the Zakaria train and his assistant were currently unknown.

Train crash in Karachi, Pakistan Show all 10 1 /10 Train crash in Karachi, Pakistan Train crash in Karachi, Pakistan People look for victims in the wreckage of the trains in Karachi, Pakistan AP Train crash in Karachi, Pakistan At least 17 passengers were killed and more than 50 injured when two passenger trains collided head-on near Karachi EPA Train crash in Karachi, Pakistan Pakistani rescue workers shift an injured passenger at the site of a collision between two trains in Karachi Getty Train crash in Karachi, Pakistan Pakistani rescue workers search for survivors at the site of a collision between two trains in Karachi Getty Train crash in Karachi, Pakistan Pakistani bysranders watch rescue workers at the site of a collision between two trains in Karachi Getty Train crash in Karachi, Pakistan A rescue worker sits beside the bodies of the victims of trains accident lying at a mortuary after two railway trains collided in Karachi, Pakistan EPA Train crash in Karachi, Pakistan Relatives affected after identifying the bodies of their loved ones EPA Train crash in Karachi, Pakistan Relatives react after identifying the bodies of their loved ones at a mortuary after two railway trains collided in Karachi, Pakistan EPA Train crash in Karachi, Pakistan Relatives after identifying the bodies of their loved ones EPA Train crash in Karachi, Pakistan Victims of train accident arrive at a hospital in Karachi, Pakistan AP

He ordered an immediate investigation which he said would be complete within 72 hours.

He said: “Facts will be brought forward, and whoever is responsible will not escape legal action and punishment”.

One eye witness, Ajab Gul, said he was on his way to work when the crash happened.

He said: “Suddenly another train came speeding in and smashed into the parked train,.

Relatives react after identifying the bodies of their loved ones at a mortuary after two railway trains collided in Karachi (EPA)

“There were clouds of dust and smog. After that we heard screams. People inside the collided trains were screaming and crying.”

People transfer an injured victim to a hospital (EPA)

Mr Gul said he had rushed to help pull 17 people, including women and children, from the wreckage but there were “many other people trapped inside... we could not get them out.”

It it is the second major accident to hit Pakistan’s rail network in the past few months.

In September at least four people were killed and 93 injured when an express train collided with a freight train near the city of Multan in Punjab province.