Prime Minister Jacinda Ardern delivered the biggest election victory for her Centre-Left Labour Party in half a century on Saturday as voters rewarded her for a decisive response to Covid-19.

The mandate means Ardern, 40, could form the first single-party government in decades and will face the challenge of delivering on the progressive transformation she promised but failed to deliver in her first term, where Labour shared power with a nationalist party.

“This is a historic shift,” said political commentator Bryce Edwards of Victoria University in Wellington, describing the vote as one of the biggest swings in New Zealand’s electoral history in 80 years. Labour was on track to win 64 of the 120 seats in the country's unicameral parliament, the highest by any party since New Zealand adopted a proportional voting system in 1996.

Ardern, 40, promised supporters she would build an economy that works for everyone, create jobs, train people, protect the environment and address climate challenges and social inequalities.

“We are living in an increasingly polarised world,” she said. “A place where more and more have lost the ability to see one another’s point of view. I hope that with this election, New Zealand has shown that this is not who we are.”

Opposition National Party leader Judith Collins said she congratulated the Prime Minister for an “outstanding result”.

Labour had 49.0 per cent of the votes, far ahead of National at 27 per cent, the Electoral Commission said, with 95per cent of ballots counted.

Ardern said she would wait until the final result to say if her government would include smaller groups like the Green Party, a former coalition partner that secured a bigger mandate.

National leaders were decimated in their strongholds by young Labour candidates who appealed to voters with progressive, democratic messages, and highlighted the party’s success in beating coronavirus.

“The last seven months of this government, all of the issues around their past promises have been put aside because of Covid-19. It’s that simple,” said deputy National leader Gerry Brownlee.

Despite the election’s tilt to the Left, Ardern “is likely to continue to chart a centrist course, largely aiming to implement incremental change that she hopes will outlast a future change in government”, because she owes her victory to Centre-Right voters who previously supported National, said Geoffrey Miller, analyst at political website Democracy Project.