Thirty-four of the 99 long-finned pilot whales stranded at Farewell Spit in Golden Bay have died since getting stuck in shallow waters on Monday.

The Kiwi press initially reported 22 of the whales have died, but 12 more died overnight.

The whales were seen close to the shore around lunchtime Monday, seven kilometres up the Spit.

Project Jonah, a volunteering organization caring for whales in New Zealand, reported 26 whales were unaccounted for, and there is no guarantee that all of them managed to swim out during high tide. It is also possible the missing whales have been swept away.

Around 50 people from Department of Conservation and Project Jonah attended to the whales immediately but they had to halt operations Monday night over lack of light and a quickly moving tide.

"The failing light and a quickly rising tide make continuing our first aid action too dangerous," Project Jonah chief executive Kimberly Muncaster told TVNZ, adding she hoped that the whales could make it back to the ocean by themselves on the high tide at 11pm.

Muncaster said Project Jonah is working closely with the Department of Conservation to assist in the whale rescue operations.

Project Jonah medics are trained to respond in whale stranding situations with necessary knowledge and equipment even in difficult conditions, Muncaster said.