US marine experts have put down a group of pilot whales after they swam ashore for a third time, despite efforts to keep them at sea.

The animals were too ill, exhausted and distressed to return to the sea after they pushed ashore once more on a marshy, remote beach near Cape Cod, Massachusetts.

So the decision was made to put down the surviving members of the pod.

Local volunteers and holidaymakers had spent two days herding the whales to sea and trying to regulate their body temperature with wet blankets and sheets.

"After two days of trying to give these animals any opportunity we could, a decision was made by the veterinarians on site to euthanise those animals that weren't already dead," said New England Aquarium spokesman Tony LaCasse.

"It's probably one of the harder decisions that anyone can make," he added.

The whales, which were tagged, were found in shallow waters at Eastham, Cape Cod, on Monday.

About 15 whales died at the first beaching.

Early on Tuesday about 45 surviving whales beached again at Lieutenant Island.

Some of the whales died after the second beaching, and those that survived were sunburnt and blistered and clearly distressed - wailing to each other.

Rescuers turned them onto their stomachs to prevent them from suffocating before high tide.

But the 30 to 35 surviving whales swam ashore again on Tuesday afternoon.

According to Teri Frady, spokeswoman for the National Marine Fisheries Service, a total of 60 whales died, including those put to death.

Pilot whale pods become stranded fairly regularly as they are sociable animals and like to feed in coastal waters.

The Cape Cod region of Massachusetts is a common site for whale beachings as its curved peninsula can trap mammals attracted by its rich source of squid, sand eels and crustaceans which whales like to feed on.