Green Party politicians are mourning the loss of the party's first female co-leader Jeanette Fitzsimons.

Since the news of Fitzsimons' death broke, tributes have poured in far and wide for her and her family.

RNZ Jeanette Fitzsimons, who led the Green Party into Parliament in the 1990s, has died unexpectedly overnight, aged 75.

Fitzsimons was a New Zealand politician and environmentalist and a former co-leader of the Greens.

She died on Thursday night. Police confirmed they attended a sudden death at Thames Hospital late last night. The matter has now been referred to the coroner.

Stuff Retired Green Party co-Leader Jeanette Fitzsimons pictured on her organic farm near Thames. (Image from 2010)

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Her husband, Harry Parke, told RNZ that her death was totally unexpected.

"Yesterday morning she was out on the farm doing stuff, she had a bit of a fall and finally ended up in Thames Hospital where she had a massive stroke and died at 9.45pm last night - very peacefully I might add," he told RNZ.

The day prior she had been using a chainsaw, Parke said. "... She worked a lot harder than I ever did. I was totally in awe of her," he said.

RNZ RNZ National's Morning Report spoke to Fitzsimons' husband Harry Parke.

Green Party co-leader Marama Davidson said that it was the "heaviest heart" that she mourned the passing of the first female co-leader of the Green Party.

"I would like to first and foremost pass on my deepest condolences to Harry, Jeanette's children and their grandchildren," Davidson said in a statement.

"We have a deep amount of love for her and her family. People across the country and the world will be feeling the loss as we all are.

"I was privileged to know Jeanette once I became an MP and then co-leader. I leaned on her mana as a rangatira of the Green Party, she helped guide my thoughts and affirm what my role is as co-leader."

JASON DORDAY/STUFF Green Party Co-leader Marama Davidson hugs TVNZ reporter Katie Bradford after a press conference on the passing of Jeanette Fitzsimons.

Davidson said Fitzsimons was what she calls "a taonga of the green movement".

"Jeanette leaves behind a remarkable legacy. She brought the climate change conversation into Parliament, and had transformative ideas around greening our electricity sector.

"She was the leading voice for a new compassionate, ecologically sustainable economics that has influenced the Government's new wellbeing approach.

"She fought for what she believed in right until the end, refusing to retire, she once said 'retirement is not really a concept I can imagine."I will miss her dearly".

Davidson also spoke about Fitzsimons at a media conference held on Thursday, where she reiterated how much of a pioneer the former politician was.

TOM LEE/STUFF The Coromandel home of Jeanette Fitzsimons.

Prime Minister Jacinda Ardern said Fitzsimons was a steward of the New Zealand environmental political movement.

In a statement Ardern said the country had lost someone completely and utterly driven by values, who embodied the notion of leaving this place better than they found it.

"Starting out in the Values Party in the 1970s, through to entering Parliament as part of the Alliance in 1996 and becoming the only Green to ever win an electorate seat in 1999, Jeanette was a ground breaker in Green politics.

"During her 14 years in parliament she was an early voice for action on issues now considered mainstream like climate change, the deteriorating state of our water and clean energy.

"She served as the Government spokesperson for Energy Efficiency and was the architect of the Energy Efficiency and Conservation Act.

"Jeanette once polled as the most trustworthy party leader in New Zealand, a fitting endorsement of her kind, caring and passionate brand of politics.

"My thoughts are with Jeanette's husband Harry, her children, grandchildren and her friends in politics and the wider green movement," Ardern said.

Parliament TV Jeanette Fitzsimons' 2010 valedictory speech.

Green Party co-leader James Shaw said Fitzsimons was somebody who embodied the different style of politics that the Greens have always stood for.

"She was never about personality politics, she was driven by what was the right thing to do."

He said she also treated everyone with respect no matter their politics, and she treated everybody with dignity.

He said Fitzsimons had immense generosity and humility. Shaw said he would miss her.

Henry Cooke/Stuff Jeanette Fitzsimons pictured speaking to media at a Green Party conference. (Image from 2018)

New Zealand First leader Winston Peters also sent his condolences to Fitzsimons' family and friends.

"Jeanette was a hugely significant figure in the formation of the Green Party, a tireless advocate for the environment, and a leader who carried herself with great dignity and conviction," he said in a statement.

"Helping to forge a new political party and going on to lead it for 14 years is a fulsome contribution that is respected by parties across the political spectrum. Jeanette was an authentic person and skilled politician.

"Our sympathies go out to the Green Party, who will be keenly feeling her loss today," he said.

Coromandel National MP Scott Simpson said: "It's a sad day for Coromandel and a sad day for New Zealand politics."

"Jeanette was always articulate, passionate and energetic about the environmental principles that she held so dear, but actually lived by, and that is a remarkable testament to her credentials," he said.

"Jeanette was a very present personality in our communities around the Coromandel. I used to frequently meet up with her at community and political events and she was always willing and happy to engage.

"I think Jeanette was much admired locally, nationally and internationally. She was very highly regarded and respected."

Thames-Coromandel District Mayor Sandra Goudie:"Jeanette was an absolute icon for the Greens movement, there's no question about it. She was respected right across the political spectrum and she treated everybody with dignity and respect.

"Certainly there are sectors of the community in which she will definitely be a sad loss, and it's a loss to our community.

"I think there will be an element of sadness that will pervade and rightly so. She was such a good person, and it's sad she's no longer with us."

JASON DORDAY/Stuff New generation Green Party member Chlöe Swarbrick gets a few bits of advice from former co-leader Jeanette Fitzsimons. Video first published in 2017.

Thames-Coromandel District councillor and environmentalist Robyn Sinclair said Fitzsimons was always supportive of her journey into local government.

"She was one of the first people to email me when we first saw the election result was very close," she said.

"She was absolutely professional and she had this real presence, so that when she was talking, her mana was such that you just wanted to listen to her.

"She never raised her voice, and she was so well-spoken in everything that she did.

"More than being a pioneer, she was an inspiration to a whole generation of people, and an inspirational person to be around.

"Everywhere she moved, there will now be a hole. The ripples of her life will extend way beyond just the political. It's going to take a long time to find a new normal."

POLITICAL HISTORY

Fitzsimons was a New Zealand politician and environmentalist. She was the co-leader of the Green Party of Aotearoa New Zealand from 1995 to 2009, and was a Member of Parliament from 1996 to 2010.

Fitzsimons resigned from Parliament in 2010 after a 13-year parliamentary career.

At the time she announced her resignation, she had just celebrated her 65th birthday and said that she wanted to spend more time on the farm and with her grandchildren.

Greg Bowker/Getty Images New Zealand Prime Minister Jacinda Ardern says the country has lost someone completely and utterly driven by values. (File photo)

Fitzsimons was believed by Green Party to be the first Green candidate in the world to win an electorate in a first past the post contest, when she won the Coromandel seat in 1999. She lost the seat the following election to National.

In 1998, Fitzsimons introduced the Energy Efficiency and Conservation Act and spearheaded Green Party negotiations for a household insulation fund.

She shared the co-leadership with the late Rod Donald, who died just weeks after the 2005 election.

After she stood down from co-leadership of the Green Party in 2009, she was replaced by Metiria Turei.

Fitzsimons then left Parliament in 2010, and was replaced on the Green Party list by Gareth Hughes.

She was made a Companion of the New Zealand Order of Merit in 2010.

Tess Brunton Former politician and Green Party co-leader Jeanette Fitzsimons has died. (Image from 2016)

Supplied Jeanette Fitzsimons pictured previously being interviewed at the Greens election party. (Image from 2017)