According to Pakistani officials, one train travelling in Sindh province had derailed and landed on another track. A second train packed with passengers then collided with it and overturned.
Rescue teams took the injured to nearby hospitals and it is thought that several are in a critical condition.
A senior official in the Ghokti district, Usman Abdullah, told Reuters it was hard to know how many people were still trapped in the train.
“There are about six to eight bogies [carriages] that are totally smashed… there is a sleeper train, AC [air conditioned] class, as well as economy class, in which there were between 47 to 50 people on this side and around 50 to 60 people on the other train,” he said.
Prime Minister Imran Khan said he was “shocked” by the accident and promised a full inquiry.
Footage from the site shows the wreckage of several carriages lying on their side. It is not clear what caused the derailment.
Several people are though to remain trapped. News agency AFP quoted a railway spokesperson as saying: “The site is far and that’s why we are facing some trouble in the rescue work.”
Pakistan has seen a string of deadly train accidents over the past years.
Local media reports says 150 people died in such incidents between 2013 and 2019.