A tourist boat capsized in southern India leaving at least 21 passengers dead on Sunday evening.

The double-decker vessel was said to be overcrowded as it was carrying around 40 people when it overturned and sank off Tamur town in Kerala state on May 7.

Local authorities said most of the casualties were women and children who were on vacation amid school holidays. The exact cause of the capsizing is still unclear.

V. Abdurahiman, Kerala minister for fisheries and harbour development, said the death toll will likely rise as operations continue to rescue the other passengers trapped inside the boat.

He said: 'More victims are believed to be trapped under the boat and have to be brought out. The boat had overturned. The reason for it is not yet known. Police will be investigating it.'

Prime Minister Narendra Modi said the families of the victims will be receiving financial aid. In a statement, he said: 'Pained by the loss of lives due to the boat mishap in Malappuram, Kerala. Condolences to the bereaved families. An ex-gratia of Rs. 2 lakh from the Prime Minister's National Relief Fund would be provided to the next of kin of each deceased.'