Bill English vows to be 'strongest Opposition party ever'

National leader Bill English, fresh off from losing his second election, has vowed to be the "strongest Opposition party that Parliament has seen".

"Almost one in two New Zealanders did support us," he said.

Despite that, it wasn't enough to secure a Government. National still needed NZ First to be able to do so - as did Labour.

On Thursday evening NZ First leader Winston Peters announced his choice: he would form a Government with Labour.

Both parties only found out the result at the same time as the public, and Mr English and National were left out in the cold.

"The Government is going to change," he admitted in a press conference later that night.

"New Zealand through the democratic process has elected a different Government and we wish them well."

When asked if he felt "robbed" in the aftermath, Mr English sidestepped the question by saying it was a "result of MMP in New Zealand", adding that the parties who had "less support than us" were able to band together to form a Government.

He said his Government left New Zealand in "great shape, by any international measure".

Mr English has now led his party to two defeats, after being thrashed by Helen Clark-led Labour in 2002.

He wouldn't confirm whether he would resign as leader after this election, as he did 15 years ago.

"That's a matter for the next few weeks for us to discuss among ourselves," Mr English said.