The railways minister, Sheikh Rashid Ahmed, said most of the deaths were passengers throwing themselves from the moving train to escape the fire.
The minister said the incident was caused by the explosion of a gas canister while passengers were cooking breakfast on a stove on the train on Thursday morning. It is illegal to bring gas canisters on to trains but the rules are frequently flouted.
“Two stoves blew up when people were cooking breakfast, the presence of kerosene with the passengers in the moving train further spread the fire,” Ahmed said.
The incident took place on a train known as the Tezgam Express, which travels between the cities of Karachi and Rawalpindi, as it was crossing through Punjab province.
Mansoor Ahmed, the assistant commissioner of the nearby city of Multan, confirmed the death toll stood at 70 so far, with more than 40 injured, many critically.
Nine people were airlifted to the burns unit at Multan district hospital. On Thursday afternoon, rescue workers and officials began sifting though the charred wreckage for victims.
Local hospitals struggled to cope with the scale of the blaze. Mansoor Ahmed confirmed the nearby Rahim Yar Khan district hospital was unable to accommodate the number of casualities, so several had to be taken to Multan district hospital, which is about three hours away.
Imran Khan, Pakistan’s prime minister, tweeted: “Deeply saddened by the terrible tragedy of the Tezgam train. My condolences go to the victims’ families and prayers for the speedy recovery of the injured. I have ordered an immediate inquiry to be completed on an urgent basis.”
Incidents on trains are common in Pakistan, where corruption, mismanagement and lack of investment have caused the railways to decline over the past few decades. Overcrowding is also a frequent safety issue.
In July, at least 23 people were killed in the same district when a passenger train from the eastern city of Lahore crashed into a goods train that had stopped at a crossing.