The Karachi express, carrying around 1,000 people, was en route to Lahore when 12 of 16 carriages went off the rails near the town of Mehrabpur. The accident occurred at around 2:00 a.m. local time [9:00 .p.m. Tuesday GMT].
"According to our estimates, 58 people were killed and 122 injured," a paramedic spokesman was quoted as saying by national media.
People still remain stuck between the carriages, and there is a high likelihood that the death toll will increase, rescuer workers said. The train was believed to have been carrying far above its intended capacity.
The Sindh province is notorious for railway disasters. At least 130 people were killed in July 2005 in the town of Ghotki when three trains collided.
A 1989 derailment in the region saw the deaths of between 300 and 400 people, and around 100 passengers were killed a year later in another crash.
