Conservation workers in New Zealand have been “popping” pilot whales “like balloons” to stop their carcasses exploding.

Around 400 whales died after one of the largest ever strandings in the country’s history.

The public has been warned about the dangers posed by “whales exploding” on Golden Beach, on the South Island, and the Department of Conservation (DOC) has cordoned off the area.

Workers spent Monday cutting holes in the animals, using knives and two metre needles, to release internal gases. It was “like popping balloons,” a DOC spokesperson told local radio.

It would take several months for the bodies to decompose and turn into skeletons.

The surviving whales were last seen swimming six kilometres (four miles) offshore on Sunday evening, according to DOC.

Clean-up begins after 350 whales die on New Zealand beach

Last Thursday, a pod of about 400 whales became stranded, with a second pod of more than 200 whales stranded on Saturday.

The precise cause is not known.

Beached whales are not uncommon on Golden Bay. Its shallow muddy waters confuse the whale's sonar, leaving it vulnerable to stranding by an ebb tide, according to marine environmental organisation Project Jonah.

Dead whales beached on the North Sea coast Show all 8 1 /8 Dead whales beached on the North Sea coast Dead whales beached on the North Sea coast Two dead sperm whales are seen washed up on a beach near Skegness in northeast England. Four sperm whales believed to be from the same pod washed up on beaches in northeast England. Three whales were found on a beach near Skegness and one died on Hunstanton beach AFP Getty Dead whales beached on the North Sea coast 50ft sperm whale beached in Norfolk The dead 50ft (14.5m) young adult male sperm whale beached in Norfolk, which was was part of a group of six spotted in the Wash at Hunstanton, is believed to have been part of a pod that stranded and died in the Netherlands PA Dead whales beached on the North Sea coast 50ft sperm whale beached in Norfolk The dead 50ft (14.5m) young adult male sperm whale beached in Norfolk, which was was part of a group of six spotted in the Wash at Hunstanton, is believed to have been part of a pod that stranded and died in the Netherlands PA Dead whales beached on the North Sea coast 50ft sperm whale beached in Norfolk The dead 50ft (14.5m) young adult male sperm whale beached in Norfolk, which was was part of a group of six spotted in the Wash at Hunstanton, is believed to have been part of a pod that stranded and died in the Netherlands PA Dead whales beached on the North Sea coast 50ft sperm whale beached in Norfolk The dead 50ft (14.5m) young adult male sperm whale beached in Norfolk, which was was part of a group of six spotted in the Wash at Hunstanton, is believed to have been part of a pod that stranded and died in the Netherlands PA Dead whales beached on the North Sea coast 50ft sperm whale beached in Norfolk Two of three dead sperm whales that have washed up on a beach in Lincolnshire, just a day after another was beached in Norfolk PA Dead whales beached on the North Sea coast One of three dead sperm whales that have washed up on a beach in Lincolnshire, just a day after another was beached in Norfolk PA Dead whales beached on the North Sea coast Photo taken from the Twitter feed of the @RNLIskegness of one of three dead sperm whales that have washed up on a beach in Lincolnshire, just a day after another was beached in Norfolk PA