At least eight people drowned when the vessel they were travelling in hit a fishing boat and capsized off the southern port city of Kochi on Wednesday afternoon.
The vessel, which was on its way from Vypin to Fort Kochi, was carrying more than 30 passengers.
Some fishermen and other people managed to rescue the rest of the passengers.
Among the dead were two women and two children. The death toll could rise three of the rescued passengers are in a serious condition, hospital officials in Kochi said. The fate of the fishing boat was not immediately known.
According to survivors, the vessel hit the fishing trawler and capsized near the shipping channel of Kochi port.
Marine enforcement and Coast Guard teams took part in the rescue operations.
The timely intervention of local residents helped avert more casualties on the eve of Onam. This was the first time such a major accident was reported from Fort Kochi.