At least 58 people are dead following the derailment of an express train in Pakistan loaded with holiday travellers.

The derailment happened at about 2 a.m. local time on Wednesday, leaving hundreds trying to escape the wreckage in total darkness.

"More than 100 people have been injured, and rescuers -- including members of Pakistan's military -- are searching through the mangled wreckage," ABC News correspondent Gretchen Peters told Â鶹´«Ã½net from Islamabad.

"They are trying to see if there are more people they can pull out. They can hear people (still) inside the wreckage."

The train was travelling from Karachi to Lahore and was about 400 kilometres north of Karachi when 12 of 16 cars came off the rails.

"The train was going at full speed. Then there was a sudden jerk and we felt the train sinking into the earth. There was chaos everywhere," said Shahid Khan, 25.

Khan, travelling with six relatives, used the light from his cellphone to find his way out.

"Unfortunately, derailments are quite common here," Peters said.

"The rail system hasn't been updated since the British colonial era, which ended 60 years ago."

The crash area is remote. People from surrounding villages showed up with carts pulled by donkeys to try and transport crash victims to hospital, she said.

The army came to help the overwhelmed villagers, and ambulances were dispatched from as far away as Karachi, Peters said.

Pakistan and other Muslim countries are currently celebrating the Islamic holiday of Eid ul-Adha.

Peters likened it to Thanksgiving in the West, a period of feasting with family.

With files from The Associated Press