UPDATE: THIRTY-nine pilot whales stranded on the northern coast of New Zealand's South Island have successfully been refloated.

Rescuers are hoping they will soon head out to sea.

About 100 whales stranded on Farewell Spit in Golden Bay around midday on Monday in the third mass stranding of the summer.

Thirty-four of them did not survive the night, but the 39, which were stranded about 7km from the base of the spit, were refloated at high tide this morning.

The remainder were spotted about 4km offshore, Project Jonah chief executive Kimberly Muncaster told AAP.

The rescuers were very happy with the progress of the 39 freed whales, which were 200m to 300m offshore about midday.

"They are doing really well. They are exhibiting typical post-stranding behaviour. They are regrouping, being very communicative with each other, rolling, stretching and touching each other.

"It looks like they are trying to work out a plan of attack and `which direction now?'"

Two Department of Conservation (DOC) boats were tracking the whales, ready to escort them back out to sea if they threatened to strand again.

About 50 people had volunteered to help with rescue efforts, with people travelling from as far as Australia, Auckland and Invercargill to take part.

DOC spokesman Nigel Mountford said the dead whales would either be buried or left to dry out in the dunes. Pilot whale bones are porous and not considered good for Maori carving.

The spot where the whales were stranded is close to where 25 were stranded early in January.

Seven of those whales died, while 65 whales died after becoming stranded in the same area in November.