At least 26 people were injured in the accident that took place at Natoli around 1.30 a.m. The Assam State Transport Corporation bus was on its way to Guwahati from Lakhimpur.
"At Natoli, the bus hit the railing of a bridge and fell into the gorge," a police official said.
Eighteen of the injured were admitted to a hospital, while the rest were released after preliminary treatment. Police said the condition of some of the injured was serious.