National Party leader Judith Collins has addressed supporters in Auckland in the wake of a devastating election result.

Greeted by chants of "Judith" as she arrived at the Royal NZ Yacht Squadron in central Auckland, Collins said she knew the night would be tough.

She thanked the party's volunteers, saying they had given their all in difficult circumstances. "We just love you ... you kept the faith," she said.

She also thanked all National voters, saying the party would repay their trust over the next three years.

"When I became leader three months ago we had to work very quickly and with confidence during a very difficult series of events," Collins said.

She had called Prime Minister Jacinda Ardern and congratulated her on an excellent result for the Labour Party.

But, she said, the new government faced tough times.

"New Zealand is in for a tough economic ride and it is going to need better fiscal policy than so far we have seen ... and I promise you, the National Party will be a robust opposition.

"We will hold the Government to account for failed promises and push on behalf of all New Zealanders to do better for all Kiwis.

"Even though tonight has been a very tough night for us all ... three years will be gone in the blink of the eye. I say to everybody, we will be back."