The train caught fire near Dunton Green, Kent, blocking both lines between Sevenoaks and Orpington.
In a series of tweets, Network Rail has confirmed that nobody has been injured and the fire has now been put out.
Network Rail engineers will now move the damaged tamper, a machine which restores the level of the track, to check for damage to the track and assess what repairs might be needed.
Network Rail estimates that it could take most of this morning to clear.
A Network Rail Kent and Sussex tweet added: We don’t know yet what caused the fire but are working with Kent Fire Rescue who are investigating. We have lots of people on site right now working to get passengers moving again and that’s our priority. We’re sorry for the disruption this has caused.
Picture: Twitter @HammertimeLH44
A commuter line linking London to the South East has been closed after a Balfour Beatty track-maintenance train caught fire in the early hours of this morning.
The fire has blocked both lines of the railway at Dunton Green in Kent, affecting services between Orpington and Sevenoaks. The tamping machine, which is used to level rail lines, had workers on board when it caught ablaze but Network Rail said no one was hurt.
A Balfour Beatty spokesperson confirmed the machine was theirs. She added: The health, safety and wellbeing of those who work with and for us remain our priority and we can confirm that there were no injuries as a result of this incident.