The train was travelling from Karachi to Rawalpindi when the incident happened.
The fire has broken when a gas cylinder being carried by a passenger exploded in the passenger train, a Pakistan Railways official has said.
Some of the dead bodies have been identified while several others are unidentifiable.
According to reports, the passengers were cooking breakfast when the blast occurred.
The fire destroyed three of the train carriages, including two economy class carriages and one business class.
Pakistan Railways Minister Sheikh Rasheed has said: “Two cooking stoves blew up. They were cooking, they had (cooking) oil which added fuel to fire.”
“Most deaths occurred when people jumped off the train,” he said.
This is the second major train accident in Pakistan this year. In July, 24 people were killed, when the Akbar Bugti Express travelling from Lahore to Quetta collided with a stationary freight train at the Walhar Railway Station in Sadiqabad Tehsil of Punjab province.