The Belgian National Railways (SNCB) train had earlier hit a car on a level crossing in Morlanwelz. While the damaged train was being hauled away, it became detached and rolled back down the line hitting Infrabel track workers.
The runaway train then gathered speed and crashed into a passenger train travelling from Namur to Tournai at Bracquegnies near Mons resulting in injuries to three passengers, the driver and the conductor.
Buses are currently replacing trains between Mons and Marchienne-Au-Pont and between Binche and La-Louvière-Centre until Infrabel has repaired the damage.
An investigation is underway to find out the cause of the accident.