The four were part of a herd that had been crossing the railway tracks as the train approached late on Saturday, about 110 miles from Guwahati, in the state of Assam.
A herd of elephants was crossing the rail tracks at Habaipur near Lumding reserve forest when the Guwahati-Silchar Express hit them last night, killing five on the spot, he said.
None of the train passengers were injured during the accident, which derailed the vehicle.
Though the NF Railways says the incident took place at a location where there was no notified elephant corridor, the forest department has already given them a list of 19 locations in three forest ranges where elephants often move on the tracks.
"Based on inputs received from forest department a speed restriction of 30kmph had been imposed and all trains were instructed to slow down while passing by". While prima facie enquiry has revealed that the train was within its stipulated speed, a departmental enquiry has been ordered to find out details of apples and adherence to protocols.
Train services were affected in the area as the carcasses of the elephants had not yet been removed.
Both forest department and NFR conceded that because of "close" coordination between officials from two sides many imminent mishaps were averted.
Earlier on December 10 a year ago, five elephants, including a pregnant female were killed when the Guwahati-Naharlagun Donyi Polo Express hit a herd crossing tracks near Balipara in Sonitpur district. Also in November previous year two elephants were killed by a train at Thakurkuchi, in the outskirt of Guwahati.