An express train crowded with holiday travelers derailed early Wednesday in southern Pakistan killing at least 56 people and injuring other 100, police said.

The train, carrying more than 1,000 people, was heading from Karachi to Lahore when 12 of its 16 carriages came off the rails near the city of Mehrabpur in Sindh province, Rahat Afzah, an information officer with Pakistan Railways, said by telephone, the Associated Press reported.

Its speed was about 250 miles per hour according to passengers surviving the accident.

"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," Shahid Khan, 25, told Associated Press.

The passengers from the train were returning home for the Islamic festival of Eid al-Adha. Some carriages plunged directly into the water.

The cause of the accident was not immediately clear and railway officials are currently investigating the scene of the accident.

"My guess is that there was some piece of rail was missing and the engine jumped the missing track and the following wagon got stuck," said Mohammed Khalid, a railway official who was traveling in one of the rear wagons that luckily stayed on the rails.

Dozens of soldiers and police officers were brought to the accident place to help tend the injured and carry them away to waiting ambulances. Moreover, people living nearby came to help the authorities and the injured people.

Rescuers had brought 56 bodies to three nearby hospitals by morning, according to Mumtaz Ali, an official from the Edhi Foundation, Pakistan’s largest privately run emergency service.

Almost 150 people were reported injured, according to Col. Abbas Malik, an army doctor.

Pakistan has a history of deadly accidents on its ageing railway system. Over 130 people died when three trains collided near the southern town of Ghotki in July 2005. That had been the worst train disaster in Pakistan in the last 15 years. A speeding train, in October struck a crowded bus at a railway crossing near Lahore, leading to 12 deaths and about 50 people injured.