WELLINGTON • New Zealand Prime Minister Bill English has claimed a mandate to form the next government after winning the biggest slice of the vote in last Saturday's election, even as opposition Labour leader Jacinda Ardern refused to concede defeat.

Negotiations could last several weeks, extending the period of uncertainty around the election that has unsettled financial markets, though analysts said any fears of radical change had been allayed by National's strong performance.

While Mr English's ruling National Party fell short of a majority and will need the support of the nationalist New Zealand First (NZ First) Party to govern, it took 46 per cent of the vote compared with 35.8 per cent for Ms Ardern's Labour Party. She would need to engineer a three-way coalition involving both NZ First and the Green Party to oust Mr English from office.

The final outcome now rests with NZ First leader Winston Peters, a 72-year-old maverick who could support either side and can be expected to extract a high price.

In return for backing a National government in 1996, Mr Peters was appointed deputy prime minister and treasurer. When he supported Labour in 2005, he was rewarded with the foreign affairs portfolio.

Mr Peters said yesterday that he still has not spoken to either major party leader.

Mr English, 55, hopes for a rare fourth term for his party, which has delivered eight consecutive years of economic growth and returned the Budget to surplus.

But a strong challenge from Labour under 37-year-old Ms Ardern has highlighted growing concerns about poverty, homelessness and the environment. And Ms Ardern says she is not throwing in the towel.

Political analyst Bryce Edwards said: "Mr English has a greater chance of forming a coalition with Mr Winston Peters, but there's absolutely no reason that there won't be a Labour-New Zealand First-Greens coalition The numbers add up either way."

BLOOMBERG, REUTERS