Railway PRO Nripendra Bhattacharya said the explosion led to the engine and eight coaches jumping the rails at around 8:30 last evening at Dhatkuchi between Rangia and Ghagrapar in the district.
Four of the coaches toppled over and fell into a three feet water-filled ditch following the explosion, he said.
A large crater beside the tracks and a huge length of fuse wire leading to a jungle were found by the Bomb Disposal Squad after the derailment.
A senior police officer said it appeared to be the handiwork of the Ranjan Daimary-led National Democratic Front of Bodoland anti-talk faction, active in the area.
The officer said at least 100 passengers were injured who were admitted to the Guwahati Medical College and Hospital.
Of the injured, 41 were in a serious condition, hospital sources said. Railway officials are supervising restoration operations at the spot with 300 labourers at work, the officer said.
A special train with 800 passengers of the Guwahati-Puri Express left Guwahati for Puri at 5:30 this morning.