Provincial Police Commander Central Province, Superintendent Patricia Leta said the loading capacity was for six passengers but a total of 16 boarded the boat.
She said least 12 people were confirmed to have survived the tragedy and there were children among the survivors
The police said the boat had been travelling from Toa to Burungia village in Central Province yesterday.
Superintendent Leta said a police inquiry will be held and police at Tulagi will work closely with relatives of the deceased and the survivors.
Two weeks ago a Central Province banana boat, with nine people on board, went missing, sparking a major search.
The people were found five days later washed up on Isabel - their destination had been Honiara.