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.
Train services were affected in the area as the carcasses of the elephants had not yet been removed.
The area where the accident occurred falls under the elephant corridor and was included in the list of 19 places where elephants cross the railway tracks at Lumding, Hojai and Lanka forest ranges.
The engine of the train was damaged and efforts were underway to restore train services at the earliest, he said.
Seventy elephants had lost their lives last year due to electrocution, speeding trains, poisoning, human attacks, and other accidents besides natural death, a forest department official said.