Forest officials said three full grown elephants died on the spot in Buxa reserve forest area when the Guwahati-Jhanjha Express rammed into them at about 6.30 PM, while another jumbo lay critically injured.
The oncoming train hit an elephant herd which was crossing the railway tracks, officials said.
The herd comprised upto 16 pachyderms and some more jumbos could either be injured or moved fast on seeing the approaching train, but the number was not exactly known due to darkness.
The railways dispatched a special train to take the passengers of the express, which lay stranded, to their respective destinations, NFR sources said.
A relief van was also sent to clear the tracks of the dead elephants.
Locals agitated at the spot alleging that the motorman of the train could have averted the mishap had he slowed down on seeing the herd crossing.
The railways, however, said the motorman probably could not see the herd before coming too close.