The missing are believed to be schoolchildren who were on their way to class when the accident happened.
Initial reports suggested there were 15 people on the boat, but only 12 have been confirmed so far. Three rescued individuals are receiving medical treatment, while the others have been discharged.
Witnesses say the boat, which didn't have a motor, was pulled by a rope between riverbanks. The rope broke due to strong currents, causing the boat to crash into a pillar of a nearby footbridge.
The river was swollen due to recent rains in the area.
Local authorities are providing support to the families of the victims. Accidents like this are rare in the region, where boat travel is common, especially for commuters looking to avoid road traffic.