Six whales have died on a remote beach in New Zealand’s South Island following a mass stranding and volunteers are racing against time to get 15 others that are still alive back to the sea.

Some 55 pilot whales washed up on Farewell Spit on Thursday. While most managed to make their way back out to sea, 15 have restranded and are now spread along about 1km (0.6mi) of the beach.

A video from Project Jonah, a non-profit working with marine mammals, showed volunteers pouring buckets of water on the whales to keep them cool.

“When the tide comes in, we’re going to have to move really quickly to bring these whales together, then move them out to deeper waters,” said Louisa Hawkes from Project Jonah.

The group is calling for volunteers to help with the refloating.