Nine long-finned pilot whales are confirmed dead after being stranded at Golden Bay, the Department of Conservation says.
At least 49 whales were stranded at Farewell Spit earlier on Monday. Forty are still alive.
DOC rangers were onsite with the whales at Farewell Spit and some members of the public were also there.
The whales were reported to them at about 9:30am on Monday by a Farewell Spit tour operator.
"Project Jonah marine mammal medics will assist with refloating the whales and caring for them on the beach, keeping them cool and wet until they can be refloated," a DoC spokesperson says.
"At this time, we're not looking for other volunteers to assist as we believe we have enough people."
Project Jonah says more than 50 trained medics attended the event, and they provided first aid to the whales before attempting to refloat them.
"Two-thirds of the 49 whales had been checked and confirmed alive. DOC says there are enough volunteers assisting and was not requesting more help," Project Jonah said in a tweet.
As high tide approached at 7pm, 40 whales were refloated by DoC and Project Jonah and were swimming about 80 metres offshore from the stranding site.
DoC will check the beach at first light to see whether any whales have re-stranded overnight.