More than 50 stranded in two locations in Golden Bay on Thursday and at least six have died.
Conservation group Project Jonah says the whales have now beached for a third time and are starting to show signs of fatigue.
It says people with wetsuits wanting to help are welcome, but it will limit the number of volunteers so as not to stress the whales.
Last night a Project Jonah spokesperson said 15 of the stranded whales were swimming freely in the bay.
The spokesperson said the remaining whales are still in the tidal zone, but are showing signs of encouraging behaviour.
The Department of Conservation which is also assisting at the site of the latest stranding said Farewell Spit, where whales frequently strand at the top of the South Island, "is a naturally occurring "whale trap" that occurs along a migratory route for long-finned pilot whales in New Zealand".
