New Zealand officials believe three people have been killed in Tonga as the navy readies two ships to assist in the aftermath of Saturday’s volcano eruption.

It came as Tongan authorities warned the death toll from the mammoth blast and following tsunami would grow – amid escalating concerns after a distress signal was issued from two isolated islands.

On Tuesday, New Zealand’s acting High Commissioner Peter Lund said state of emergency had been declared in Tonga, and a massive cleanup operation was underway on Tongatapu and the capital Nuku’alofa, blanketed in ash from the blast.

Mr Lund confirmed reports the body of missing British woman Angela Glover, 50, had been found, and the likelihood of two other deaths.

“I understand in talking to our police advisor this morning, unconfirmed reports of up to three fatalities,” he told NZ television station Tagata Pasifika.

“Here on Tongatapu it is very sad some fatalities have been reported.

“We were spared great loss of life. Most people are safe and now having to face a big cleanup and taking things day by day.”

Earlier, the United Nations said a distress signal was detected in an isolated, low-lying Ha’apai islands group, adding it had particular concerns about Fonoi and Mango islands. According to the Tonga government, 36 people live on Mango and 69 on Fonoi.

Angela Glover, left, was running a charity for dogs in Tonga when she was swept away by Saturday’s tsunami.

A satellite image posted by the UN Office for the Co-ordination of Humanitarian Affairs indicated there was damage to scores of structures on Nomuka island.

New Zealand sent a military P-3K2 Orion aircraft into Tongan airspace on Monday on a reconnaissance mission, feeding back its findings to the Tongan government.

“Imagery and details have been sent to relevant authorities in Tonga, to aid in decisions about what support is most needed,” NZ Foreign Minister Nanaia Mahuta said.

However, the country’s main airport remains off-limits to incoming flights due to ashfall on the runway.

In the meantime, New Zealand is sending both the HMNZS Wellington and HMNZS Aotearoa on the three-day sail to Tonga beginning Tuesday.

Defence Minister Peeni Henare said the Wellington would carry hydrographic survey and diving teams and a Seasprite helicopter, and the Aotearoa would take “bulk water supplies and humanitarian and disaster relief stores”.

“Water is among the highest priorities for Tonga at this stage and HMNZS Aotearoa can carry 250,000 litres, and produce 70,000 litres per day through a desalination plant,” he said.

A Hercules C-130 aircraft will also deliver relief once the runway is cleared.

Tweet from @NZDefenceForce

Australia also sent a Defence plane to survey the damage on Monday, with further support on the way.

Pacific Minister Zed Seselja said critical supplies such as food, water as well as communications and clean-up equipment would be flown in on an ADF C-130 once the airport can reopen.

“There is still a significant amount of ash at the airport. It was hoped the airport might open today, but that’s more likely now to be tomorrow,” Senator Seselja told the Nine Network.

“We’ve offered $1 million in assistance at the moment, we’re looking to hear back from the Tongan government in some more specific detail.”

Australia will send further supplies on HMAS Adelaide as early as Wednesday.

Mr Lund said the “huge cleanup operation” from widespread ashfall had begun in earnest.

“The government here has declared a state of emergency,’ he said.

“They are used to dealing with tropical cyclones. A tsunami … is a whole new challenge.

“They’re making progress. Roads are being cleared. Buildings are being cleaned up … Nuku’alofa is trying to get back to normal.

“There’s a priority on getting the runway cleared so that emergency supply flights … from NZ and Australia can enter the country.”

The New Zealand government has also upped its initial aid allocation to $NZ1 million ($A940,000), promising further assistance to come.

A major underwater telecommunications cable was damaged in the tsunami, and is expected to take at least two weeks to repair.

Senator Seselja said work was under way to get communication access to the Pacific nation.

“We’re working with Telstra to try and make sure we can get temporary equipment, so some better on-the-ground equipment can exist.”

-with AAP