The incident occurred Wednesday as the bus was traveling from the state of Assam through hilly Meghalaya to neighboring Tripura, the Hindustan Times reported.
Officials said many of survivors were seriously injured, raising the likelihood of the death toll going up.
Many of those killed died at the scene, while the others succumbed at a nearby community center, a police official told the newspaper. Some of the injured were taken to a hospital in Assam.
Initial reports said failure of the vehicle's brakes might have caused the disaster, but the Times quoted police as saying they also were looking into whether the driver, whose fate was not immediately known, had been under the influence of alcohol.
"We are not sure if the driver of the privately owned bus escaped or is among the dead or injured," a police officer at the scene said.
Search operations were hampered because of wet and slippery conditions at the scene where landslides are common because of constant rains.