An express train crowded with holiday travelers derailed in southern Pakistan on Wednesday, killing at least 58 people and leaving hundreds of terrified survivors to claw their way out of the wreckage in total darkness.

The train, which derailed about 2 a.m., was loaded with an estimated 900 passengers, many of them heading home for the Islamic holiday of Eid al-Adha.

Dozens of soldiers and police helped tend the injured and carry them away to waiting ambulances, as hundreds of people from the surrounding villages looked on. Army engineers used two cranes and cutting equipment to free the last survivors.

Passenger Mohammed Yusuf sat on a pink blanket next to a pile of discarded shoes and clothes, wailing in grief at the death of his younger brother.

He said his wife, two children and another brother were injured and taken to a hospital but their conditions were unknown. Yusuf, 26, said his brother survived the impact and was crying out in pain, but that he had been unable to free his trapped leg.

"It's unbearable. Don't say that he is dead," Yusuf pleaded as other relatives tried to console him.

The train, which was full but not overcrowded, was speeding from Karachi toward Lahore when about 12 of its 16 cars came off the rails near Mehrabpur, about 250 miles north of Karachi. It was unclear what caused the accident.

Shahid Khan, a 25-year-old who had been traveling to Lahore with six of his relatives, said he used the light from his cell phone to find his way out.

"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 Khan, sitting next to bundles of luggage he had salvaged from a cars lying on its side in the field.

By midmorning, rescuers had brought 58 bodies to three nearby hospitals, said Mumtaz Ali, an official from the Edhi Foundation, Pakistan's largest privately run emergency service.

Col. Abbas Malik, an army doctor, said about 150 people were injured.

Mohammed Khalid, a railway official who was traveling in one of the rear cars that stayed on the rails, said he suspected a problem with the track — possibly sabotage — caused the accident.

"My guess is that there was some piece of rail was missing and the engine jumped the missing track," he said.

After the crash, a section of one of the rails had been torn loose. The engine came to a halt about a mile up the line.

Deadly accidents are a regular occurrence on Pakistan's colonial-era railway network.

A speeding train struck a crowded bus at a railway crossing near Lahore in October, killing 12 people and injuring about 50 others. About 130 people died in July 2005 when three trains collided in southern Pakistan.