Rescue teams from Sukkur were reportedly dispatched to start repair work after the incident.
Sukkur Railways Divisional Superintendent Jamshaid Alam told Dawn News that the Jaffar Express was travelling from Peshawar to Quetta when the explosion occurred.
“Following the blast, train operations have been suspended,” Alam said, adding that passengers “faced serious difficulties due to the train’s derailment”.
Railway officials said it may take upto five years to restore the line.
The Sindh government has initiated an investigation into the issue.
In March, the train was hijacked and took 400 passengers as hostages.