About 300 have already died at Farewell Spit, on the South Island, in one of the worst such cases in the country.
Hundreds of locals and conservation department staff have been trying to save the survivors since early Friday morning, and have formed a human chain to refloat the whales.
Scientists do not know what exactly causes whales to beach themselves.
But it sometimes happens because the whales are old and sick, injured, or make navigational errors particularly along gentle sloping beaches.
Sometimes when one whale is beached, it will send out a distress signal attracting other members of its pod, who then also get stranded by a receding tide.