The authorities in Tonga now say 85 people are missing and feared drowned after an inter-island ferry sank, BBC reported.
The probable toll rose from earlier estimates of 64, after it was found 141 people were on board the Princess Ashika when it went down on Wednesday.
Fifty-four people have so far been rescued and two bodies found.
Teams of divers from Australia and New Zealand have arrived at the site, 90km (55 miles) from the capital, Nuku'alofa, to search for bodies.
"The first part of our operation is going to be reconnaissance, so that's going to involve getting out there with our autonomous underwater vehicle," New Zealand commanding officer Lieutenant Commander Andrew McMillan told Radio New Zealand.
The ship is lying in 35 metres (115 feet) of water, but it is near the edge of shelf which drops off to depths of 150 metres.
Two bodies have so far been recovered, including a British man identified as Dan MacMillan, 48, who had been living in New Zealand.
Five other foreigners - German, French and Japanese - are among the missing.
"This marine disaster is a tragedy of huge proportions for this country," said police commissioner Chris Kelley.
"The news is not good. We now have the names of 141 people who were on the Ashika, as a result of statements taken from survivors... and that number may be more," he added.
Most of those missing are women and children who were in cabins below decks, while all the survivors are men who were travelling on deck.
The cause of the sinking was unknown, but Transport Minister Paul Karalus said the ship had been recently inspected and there was "no question about its seaworthiness".
It was licensed to carry 200 passengers and crew, said the state-owned Shipping Corporation of Polynesia.
The ferry had been travelling from Nuku'alofa to outlying northern islands of Tonga when it sent a mayday call at about 2300 on Wednesday (1100 GMT).
Those who managed to make it to lifeboats say the ferry rolled in heavy seas and sank within minutes.
"All the stuff, containers everything, was moved to one side and the ship starts to turn upside down," said survivor Pau Tupou.
"It is only one minute and the ship was gone down."
The tragedy has rocked the tiny nation of 120,000, which consists of 170 islands dotted over 748 sq km (289 sq miles) of the South Pacific Ocean and is heavily reliant on ferries.