Wildlife service personnel examine the carcasses of nearly 200 whales on the west coast of Tasmania, Australia, on September 23, 2022. The whales were found beached the previous day, with only a few surviving. Photo: AFP

About 500 pilot whales have died in mass strandings on New Zealand's remote Chatham Islands, the government said on Tuesday after ruling out a rescue effort in the area's shark-filled waters.

Two "super pods" of the dolphin-­related cetaceans beached on two islands in the remote chain and survivors were euthanized, according to the Department of Conservation.

On Friday, 250 beached pilot whales were found at Chatham Island, and then three days ­later another 240 were reported on Pitt Island, the government said.

The locations - far from the New Zealand mainland - made a rescue operation impossible, authorities said.

"Due to the risk of shark attack to both humans and the whales, the surviving whales were euthanized by our trained team to prevent further suffering," said Dave Lundquist, a government technical marine advisor. 

"This decision is never taken lightly, but in cases like this it is the kindest option."

The bodies will be left to decompose naturally on site.

Mass strandings are not uncommon on the Chatham Islands, where the largest recorded beaching involved an estimated 1,000 whales in 1918.

In 2017, there was a mass stranding of almost 700 pilot whales.

Scientists do not fully understand why mass strandings occur, but some researchers think pods go off track after feeding too close to shore.

Pilot whales are highly sociable, so they may follow pod-mates who stray into danger.