Whale

Officials say vets took the decision as the four-metre (13ft) mammal was being moved in a refrigerated truck.

Overnight, rescuers spent nearly six hours lifting the 800kg (1,763lb) whale from the river using a crane and nets.

They had planned to release the animal in the sea but its health deteriorated after failing to eat.

"It is with heavy hearts we announce that the beluga did not survive," Sea Shepherd France conservation group wrote in a Twitter post on Wednesday.

"We are devastated by this tragic outcome that we knew was very likely," it added.

The company, Raw Mana, has announced plans to lengthen the runway of Lupepau'u Airport in Vava'u, to allow large aircraft to fly in, direct to the hub of Tongan tourism.

The company is also planning to upgrade the terminal and build a renewable energy power station to supply the electricity the expanded complex will need.

RNZ Pacific correspondent, Kalafi Moala, has spoken with one of the principals in Raw Mana, but he said it remains a mystery where the money will come from.

In a statement to the ABC, the Australian Department of Defence confirmed that "as HMAS Sydney was berthing alongside Naval Base San Diego in California two deceased whales dislodged from her hull beneath the surface".

The department said the Australian and US navies were cooperating with local marine authorities and other agencies to review the incident.

"The navy takes marine mammal safety seriously and is disheartened this incident occurred," a Defence spokesperson said.

Naval Base San Diego has secured the whale carcasses with booms until they can be removed.

The whale was first seen in the Northern Territory (NT) river over a week ago, prompting fears it may get stuck in shallow waters or hit a boat.

Two others also swam into the East Alligator River for a short time before returning to their sea migration.

The remaining whale managed to find its way out over the weekend during high tides, Parks Australia said on Monday.

It is the first known instance of humpback whales in the river in the Kakadu National Park, on the country's northern coast.