Volunteers sing to stranded whales as attempts are made to push them back out to sea.

With daylight fading, rescuers at Farewell Spit face an anxious wait to see whether the 80 to 90 whales stranded there survive the night.

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Experts and hundreds of volunteers spent Friday fighting to keep surviving whales alive after about 416 of them beached themselves at Farewell Spit in Golden Bay. It is New Zealand's third-worst whale stranding.

MARTIN DE RUYTER/FAIRFAX NZ The view from the air shows the overwhelming scale of the stranding.

Department of Conservation (DOC) Golden Bay operations manager Andrew Lamason said more than 100 whales had been refloated around high tide on Friday morning.

READ MORE:

* Live: Hundreds of whales dead

* Why whales strand themselves, and how to help

* Video: Devastating vision from Farewell Spit

* Photos: Whales as far as the eye can see

The refloat had been partially successful with about 50 whales out swimming in the bay, but the remaining 80 whales had re-stranded on the beach.

Lamason said volunteers would keep the beached whales comfortable until dark. The situation would be reassessed early on Saturday morning, with another attempt at refloating any remaining stranded whales at high tide around lunchtime on Saturday.

Lamason said latest reports were that an estimated 70 per cent of the whales had died overnight. While rescuers managed to refloat the survivors for high tide at 10.30am, the whales began re-stranding before noon.

A Project Jonah worker said they would be at the scene with buckets and volunteers all afternoon.

Some volunteers have been at the mass stranding all day, and the base of the spit is strewn with hundreds of whale carcasses.

Many of the whales were upright and trying to swim and thrashing around. That was a good sign, but as the tide went out volunteers needed to try to keep the whales upright rather than on their sides.

The next high tide would be about 11.30pm and volunteers would be asked to leave when daylight starts to fade. They would most likely be back at the site on Saturday.

MARTIN De RUYTER/Stuff.co.nz Aerial footage shows the scale of the whale stranding at Farewell Spit

About 300 whales have died, however witnesses report about 120 were still alive.

The atmosphere at the stranding had been described as sombre, but also peaceful and collaborative.

The overcast cool conditions was one factor in the whale's favour as their delicate skin can blister in the baking sun.

AARON WOOD/STUFF.CO.NZ There's no one reason why whales become beached.

'THE SADDEST THING'

Peter and Ana Wiles were among the first volunteers to arrive at the spit. All around them were the bodies of whales, and the soft whistling of the few to survive.

As the waves pushed the bodies of whales against the beach, the couple said there was the occasional cheer whenever volunteers managed to refloat one of the survivors.

NINA HINDMARSH/Stuff.co.nz Hundreds of pilot whales have died after a mass stranding on Farewell Spit.

Struggling to understand such a tragic loss in nature. At whale stranding in GB today pic.twitter.com/XzkmfuwBKq — Damien O'Connor (@DamienOConnorMP) February 10, 2017

Department of Conservation staff, Project Jonah volunteers and members of the public formed a human chain at high tide and helped to turn around any of the whales that were heading back to shore.

They were warned that the whales could become aggressive and to keep clear of their mouths and tails.

NINA HINDMARSH/FAIRFAX NZ It was the third-largest stranding on record. A thousand whales stranded on the Chathams in 1918.

"There was no aggression from them, I think they fully understand we were trying to help," Ana Wiles said.

MAMMOTH EFFORT, BUT CAUSE NOT KNOWN

An army of about 400 volunteers were working on rotation on Friday afternoon, keeping the surviving 120 whales upright and wet until the tide came back in.

NINA HINDMARSH/FAIRFAX NZ The whales were stranded about 1 kilometre from the base, on the inside of Farewell Spit.

By 2.30pm many volunteers had been in the water since the early morning. Due to the remote location of the stranding, DOC said anyone wanting to volunteer had to be fit, strong and bring plenty of food and water. Volunteers also needed warm clothing and sun protection

Project Jonah said there were many reasons for whales to strand.

If they were old, or sick, a whale might struggle to keep up with the pod. Underwater explosions caused by sonar, seismic testing or underwater sea quakes could also have an impact on them.

Nina Hindmarsh The whales

When chasing prey, such as squid, it was possible for whales to accidentally beach themselves.

The strong social bonding of whales meant if a few became stranded, they may draw in the rest of the pod.

DISPOSING OF THE DEAD

DOC marine species and threats manager Ian Angus said DOC, local council and iwi would work together to remove the whale carcases.

A few whales would go to Massey University, where experts would perform necropsies, or animal autopsies.

This would help shed light on why they whales stranded.

The remaining carcasses would most likely be buried locally or left to be washed out to sea and decompose on the sea floor.

It would come down to balancing iwi wishes with what was practical, he said.

Dead whales were often left on the beach to be washed out to sea, where they decomposed on the ocean floor.

Once a carcass sinks, it becomes home to scavengers.

Sharks would then consume the whale's easily accessible flesh. When the bulk of muscle and blubber was gone, organisms like snails, worms and bacteria, would settle in.

NECROPSIES TO BE PERFORMED

A Massey University lecturer has gone to Farewell Spit to perform necropsies on the whales.

Senior lecturer in wildlife health Stuart Hunter will determine if there was an underlying reason why such a large number of whales stranded and died in such a short space of time.

"It's not unusual for pilot whales to strand en masse but this stranding is unusual due to the sheer number of whales involved and in such a small amount of time," Hunter said.

Pilot whales were well-insulated with blubber and they decomposed quickly, so necropsies would need to be performed as quickly as possible, he said.

"Necropsy involves examination of the internal organs to look for signs of infectious disease and trauma.

"Ideally we will take small samples of the internal organs to examine under the microscope to determine what further tests should be undertaken. It's difficult to say when we'll know for sure, but it's likely to be weeks rather than days."

FEARS OF RE-BEACHING PROVED RIGHT

By 11am, Golden Bay operations manager Andrew Lamason said they'd successfully refloated the surviving whales, but at that stage there were concerns they might restrand.

"We've done this before though and we do have a horrible feeling they'll come back onto the beach," he said earlier.

Lamason said plenty of volunteers had turned up with good attitudes and were well-equipped with wetsuits.

"It's cold, we've had reports of people being very cold so that's a bit of an issue but there has been a really good response. Last I heard there were probably more cars in the carpark than whales on the beach."

Project Jonah general manager Daren Grover gave a briefing to dozens of volunteers in the carpark at Farewell Spit.

﻿Grover warned volunteers not to touch the whales' teeth or tails. He also said it was possible the whales had died from an infection and advised people not to breathe in anything expelled from the whales' blowholes.

'IT'S A BIG ONE'

This was the third-largest stranding on record. A thousand whales stranded on the Chathams in 1918.

The whales were stranded about one kilometre from the base, on the inside of Farewell Spit.

Lamason said the whales were first spotted swimming close to shore by a DOC ranger in the area late last night. At first light this morning the stranding was confirmed.

"It's a big one," Lamason said.

He asked rubberneckers to stay away from the site.

"We want to be in the business of saving whales, not people," Lamason said.

The long, curving spit is a prime site for whale strandings.

STRANDING IS ON AN 'OVERWHELMING' SCALE

The atmosphere at the scene is emotional and subdued. Volunteers tasked with trying to save the remaining whales are tackling the job with determination and urgency.

The whales were "thrashing around" and volunteers had to be careful.

The whales are spread out over a huge distance about 300 metres out to sea and the scale of the stranding was overwhelming.

The Golden Bay community responded to the plea for volunteers with hundreds turning up in cars and busloads to try and save the mammals