The blast killed four children in the same family and derailed the Khushal Khan Express, the Express News reported.
The blast took place near Thul station and disrupted a train en route to Peshawar from Karachi.
One witness said up to 200 people were injured, three of whom were reported to be in critical condition.
An investigation has been launched into the attack, the Express News said.
Notable deaths of 2014 [PHOTOS]