The whales beached on a sandbar at the mouth of the Okuru River near Haast overnight.
Whale saving group Project Jonah were notified of the stranding late last night.
It has a team on the ground at the remote river mouth working to save the animals.
High tide will occur at 2.31pm this afternoon, and it's hoped the remaining whales will head back out to sea on that tide.
Project Jonah says it is a very isolated location with limited access to communications.