Supporters cheer as they watch the results come in for the general election between incumbent Prime Minister Jacinda Ardern and a challenger Judith Collins during the New Zealand Labour Party election night event in Auckland, New Zealand, Oct 17, 2020. [Photo/Agencies]

WELLINGTON - Prime Minister Jacinda Ardern's centre-left Labour Party won a landslide victory in New Zealand's general election 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 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.

If Labour wins more than half the seats, Ardern could form the first single-party government under the current system.

Ardern came out of her home in Auckland, waved and hugged gathered supporters. Opposition National Party leader Judith Collins said she had called the prime minister to congratulate her for an "outstanding result".

Labour had 49.0% of the votes, far ahead of National at 27%, the Electoral Commission said, with 77% of ballots counted in an election that was largely a referendum on Ardern's aggressive handling of COVID-19.

"People were very grateful and very happy with how we've handled COVID, they like the shape of the plan that we’ve got going forward from here for the economy," said Finance Minister Grant Robertson, a top Labour MP.

Geoffrey Miller, analyst at political website Democracy Project, said the victory was "very much a personal triumph for Jacinda Ardern's 'superstar' popularity and brand."

Of Ardern's current coalition partners, the nationalist New Zealand First Party had 2.6% and the Green Party 7.6%. If she is unable to form a Labour-only government, she is expected to continue to rely on the minor Greens while jettisoning New Zealand First.

A Labour-Green coalition would be the first fully left-leaning government since the 1970s, a scenario that National's Collins warned would mean more taxes and an environment hostile to business.

Ardern has pledged to raise taxes on top earners, while Collins promised short-term tax cuts, but they have otherwise shown few major differences on policy.