Primary investigations suggest the driver lost control of the vehicle, the police said.

"A Malda-bound public transport bus fell off the Nalini Buske bridge into the Gobra canal in Balirghat area around 6 a.m. Four people have been killed," a Daulatabad police station official said.

"Two bodies were found floating in the canal. Ten persons were rescued, of which two succumbed in hospital," he added.

West Bengal Chief Minister Mamata Banerjee rushed to the spot along with Transport Minister Subhendu Adhikari and announced a compensation of Rs five lakh each to the bereaved families.

"It is a very unfortunate incident. I announce compensation of Rs five lakh for each bereaved family and Rs 50,000 to Rs one lakh for the injured," Banerjee said.

Earlier in the day, angry locals pelted police with stones and torched two police vehicles, accusing them of arriving late for rescue operations. Stones were hurled at a fire tender that was sent there to put out the fire.

Police lobbed teargas shells and baton-charged the protesters.

Hundreds of villagers as well as anxious relatives of the passengers gathered on the canal banks as four cranes were pressed into service to fish out the bus submerged in the water.