New Zealand's new opposition leader David Cunliffe said Monday he's moving to a "war-footing" ahead of elections next year.

Cunliffe also criticized popular Prime Minister John Key in his first major media briefing.

The Labour Party hopes Cunliffe will revive its fortunes after they languished under David Shearer, who quit as leader last month.

Asked what he thought of Key's leadership, Cunliffe said, "I think it sucks. And I think it's time to change it." He didn't elaborate.

Cunliffe has said he wants to raise the minimum wage and increase taxes on the wealthy.

"We'll be taking the fight to the government," he said. "They are on notice that their easy days are over."

Key said he expects Cunliffe to prove a more articulate and forceful opponent than Shearer. But he added that Cunliffe appeared already to be failing on his pledge to keep the arguments about policies and not personalities.

Polls indicate that Key's center-right National Party remains the most popular single party, but that it doesn't have as much support as the Labour and Green parties combined, which could form a left-leaning coalition.

"I treat any leader of the opposition with respect, and if you don't you're pretty silly as a prime minister and it comes at your own peril," Key said Monday. "And this is a really tight election, we know that."

Cunliffe is a former diplomat and health minister who has a master's degree from Harvard Business School.