Around 15 persons, mostly labourers, were going in the boat from Kasira to Nagadia village in the Deoli police station area when the tragedy occurred at 10 A.M., they said.
While four of the boat's passengers were rescued by villagers and a rescue team, operations are in full swing to trace the remaining three or more missing persons, they said.
The District Collector and Superintendent of Police of Tonk have rushed to the spot.
The exact cause behind the mishap is yet to be ascertained, police said, adding that the eight bodies have been recovered.