Image copyright AP Image caption A conservation worker tends some of the beached whales

Rescuers are racing against the clock to refloat about 90 stranded pilot whales after more than 100 died on a beach on New Zealand's South Island.

The rescuers and volunteers at Farewell Spit, Golden Bay, managed to shepherd many mammals into deeper water, only for them to again run aground.

Conservation officials believe they have one last chance to refloat the whales on the high tide.

If that fails, the mammals may have to be put down.

The rescuers are now trying to keep the distressed whales comfortable by pouring water over them.

Those mammals who died are believed to have suffered great physical and emotional trauma.

Local conservation ranger Mike Ogle said it is the biggest beaching incident in 10-15 years.

"Because there's just so many whales, there are a couple of spots where a lot would gather together and that's kind of problematic from the aspect that you can't get in there, it's just too dangerous," he said.

Farewell Spit has been the location of many whale beachings.

Experts say its shallow waters seems to confuse whales and hinder their ability to navigate.

Once they are stranded, whales can suffer from dehydration and sunburn.

Pilot whales can grow to about 20ft (6 metres) and are the most common species of whale in New Zealand's waters.

Andrew Lamason from the Department Of Conservation said it could take days to refloat the whales and even then there would be no guarantees they would survive.

"We've had plenty times in the past where the pods have gone out to sea and turned around and come back again," Mr Lamason said. "We're preparing for a big few days."

Scientists do not know what causes groups of whales to beach themselves.