Twenty pilot whales died and another 30 were rescued after getting stranded on the south-western coast of Iceland on Friday.

This comes only two weeks after a similarly unexplained mass stranding had already killed dozens of the long-finned cetaceans.

Volunteers from a local search and rescue squad worked through the night on Friday, trying to keep the animals in wet conditions, waiting for the high tide to come in again.

“They were lying all around here (…) but you could hear them breathing and could see their movements. So we brought blankets and towels and such, and we had water pumps to pump seawater on the animal,” said Elva Tryggvadóttir, director of rescue operations

“Then we sort of had to learn how to behave around the whales; it´ is not something that rescue squad members normally do, so it was a new experience for all,” Tryggvadóttir added.

Edda Magnusdottir, a marine biologist, said the whales were likely chasing a school of mackerel near the coastline when they got stranded.

She added the whales’ weight — about 1,000 kilograms — made them particularly difficult to rescue.