As the death toll from the Princess Ashika tragedy is now upgraded to 93, there are grave concerns that the wreckage of the ferry may never be found.

Radio New Zealand reports that the Tonga Police Commander Chris Kelly said the cause of the sinking is still unknown and warns the Ashika may never be found.

Marine Investigators from New Zealand and Australia are expected to start an inquiry to try and determine what could have caused the tragic incident as the search for the Ashika continues.

Divers from the Royal New Zealand and Australian Navies arrived on Saturday to try and locate the wreck, however they were unable to reach the sea bed on their first dive. The Princess Ashika is believed to be in 36 meters of water.

The number of passengers believed to have been on board has risen from 141 to 149. With 54 rescued and only two bodies recovered, that leaves 93 people unaccounted for.

Commander Chris Kelly said the final number could be even higher and they are continuing to analyse information about unrecorded people on board the vessel which had a manifest showing only 79 passengers and crew.