Police said the accident took place when the high speeding bus, which was on its way from Goalpara town to Guwahati, slid off the road and fell in a ditch near Chandamari under the Aagiya police station.
One of the dead has been identified as Fulsan Ali, while the identity of the other two is yet to be ascertained.
Among the injured, seven have been shifted to the Guwahati Medical College and the others have been admitted to nearby hospitals.