New Zealand Prime Minister Jacinda Ardern on Tuesday called an election for September 19, in a contest that will test whether her support at home matches her widespread popularity overseas.

Ardern's centre-left Labour Party-led coalition came to power in 2017, and is seeking a second term.

"I will be asking New Zealanders to continue to support my leadership and the current direction of the government, which is grounded in stability, a strong economy and progress on the long-term challenges facing New Zealand," Ardern told a media conference.

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Ardern won a surprise victory in 2017 after a campaign focusing on positive messaging and connecting directly with voters.

Global praise

The 39-year-old leader has since won praise globally for her views on issues such as women's rights, climate change and diversity. She became a mother while in office and was widely praised for her sensitive response to the Christchurch mosque attacks last year that led to a swift tightening of gun laws.

Ardern said last week that her party would wage a "relentlessly positive" 2020 election campaign again, announcing her party had signed up to Facebook's advertising transparency tool to fight misinformation.

But her government has grappled with issues, including housing, urban poverty, immigration, jobs and economic growth, which are all expected to be key election concerns.

Two opinion polls in October suggested support for her ruling coalition at its lowest since 2017, and her own sky-high popularity was waning.

Opposition leader Simon Bridges has led the centre-right New Zealand National Party into a more populist territory, attacking Ardern over a land dispute with Maori groups and attacking the gun buy-back scheme introduced after Christchurch.

The government announced infrastructure projects worth 12 billion New Zealand dollars ($7.9bn) last month, boosting capital spending to its highest in 20 years, as it seeks to fire up the economy.

"We will be asking for a further term to get the job done," Ardern told the news conference.

In addition to electing the next government, New Zealanders will also take part in a double referendum at the 2020 polls, as they vote on whether to legalise recreational cannabis and euthanasia.

The parliament will be officially dissolved on August 12 and until then the government will function as usual, Ardern said.