There were thousands more in Auckland and Christchurch.
The turnout was so strong, it prompted Climate Change Minister James Shaw to suggest the Government should consider lowering the voting age.
"I think when it comes to climate change and what's going on over the course of the next 30 years… it's clear that young people want to participate in the political process – that's what today is an expression of."
Zazie-Rea Taylor – an 11-year old girl from Wellington, told those gathered in Wellington she was addressing the protestors because her "future depended on it".
"Despite what some people might think, I would actually rather be at school today," she said.
"I would also prefer it if world leaders, politicians and all of society were taking the urgent action needed to stop climate change."
Although kids dominated those gathered on the front lawn of Parliament, the organisers gave an opportunity for some adults to speak as well.
The highlight of those speakers in Wellington was Shaw – who the day before had been assaulted in a Wellington park.
He was sporting a black eye and, speaking to Newstalk ZB before his address to the thousands gathered, said he was "delighted to see so many students protesting today".
He received rapturous applause as he made his way to the microphones to address the crowd.
"Today is your day – I just want you to take a moment to look around you… because this is the largest crowd marching for climate change."
The crowd in Wellington today was even larger than the one that gathered before the Paris Climate Agreement was signed in 2015.
Shaw said the politicians have been talking about climate change for 30 years – "almost all of my life and almost twice as long as most of you have been alive".
"It is time for the talking to stop, and time for the action to start."
That is why, Shaw said, the Government was committed to passing the Zero Carbon Act this year – "so that for the first time, we have a legally binding commitment to staying within 1.5 degrees of global warming".
"If we do not, we do not have a future."
Prime Minister Jacinda Ardern said the Zero Carbon Act was "ground-breaking legislation.
"It's technical and difficult legislation we are working hard to finalise. Once we lock down the remaining details we will be in a position to announce the timeframe for the Bill's introduction.
"I'm very keen to see it finalised and completed by the end of this year."
She acknowledged those students who turned up at the marches across the country today.
"My message is simple, we hear you and we're getting on with setting a path for carbon neutrality.
"Please keep bringing as many people as you can with you, because we simply won't achieve our goals alone."
Not long before speaking to the crowd, Shaw's office issued a statement with a head a headline reading: "Ministers priorities consultation on climate change".
The terms of reference for the Interim Climate Change Committee have been changed and mean the group would now deliver its two key reports, one on agriculture and one on renewable electricity generation, directly to the Minister for Climate Change.
"This will allow the Government to consider the findings and act with necessary pace," the statement said.
"We know timing is tight. This is because now is our best chance to take action. These changes will set the foundations for New Zealand to move forward on ways to tackle the impact of our changing climate," Shaw said.
