Auckland Council has joined other cities in declaring a climate change emergency.
Mayor Phil Goff said he didn't want to leave future generations the "rotten legacy" of climate heating.
"We have an obligation to act, and it would be irresponsible and reckless, not to act," Goff told a council meeting on Tuesday.
While the declaration is largely symbolic, it signals the start of a more urgent and focussed approach by councillors to curbing greenhouse gas emissions.
The council separately agreed to seek public views on an "action framework" that could lead to costed initiatives in next year's budget.
A series of groups, predominantly young people, including Para Kore Ki Tamaki, Waitematā Low Carbon Network, Extinction Rebellion, Generation Zero and the Auckland School Strike Group urged councillors ahead of the debate to make the move.
"It's political will preventing the urgent action needed," said Rose Gee of the Extinction Rebellion, which has driven efforts for emergency declarations to be made.
Gee criticised the council's urgency, with plans that had "long timeframes, and soft terminology like 'encouraging' action".
"You are a step behind," Sarah Thomson from Waitematā Low Carbon Network told councillors ahead of their deliberation.
"You need to be a step in front - and you need to be changing public opinion," she said.
Councillors speaking in favour of the declaration were repeatedly applauded by 90 members of the public who attended.
Goff asked one group of young people appearing at today's meeting, what they considered the priority action the council could take.
"Make public transport fossil-free and reduce the cost - the time we spend sitting in traffic, that's your emissions there," said Sidd Mehta, of Generation Zero.
In a statement after the vote, the council said climate change "does not satisfy the definition of an 'emergency' under the Civil Defence and Emergency Management Act 2002, and that a declaration of a 'climate emergency' has no other inherent statutory or legal implications".
"However, such a declaration may further highlight Auckland Council's belief in the importance and urgency of addressing climate change."
Auckland Council is a member of the global C40 Cities Climate Leadership Group, and on paper is committed to policies that will help limit global warming to 1.5 degrees.
Penny Hulse who chairs the Environment and Community Committee and who has led the climate change work, said real action was needed.
"We can either sleepwalk to disaster and completely let down our grandchildren and their children, or we can carry on some of the good work that's happening and do what's actually required of us," she said.
Hulse defended criticism from some councillors that little had been done, pointing to those who had voted down past initiatives such as higher density housing, and derided plans to lower speed limits.
"Voted down by popular influence by some of our communities, who still deny climate change," she told the meeting.
Councillor Daniel Newman warned of the danger of "business as usual", and argued that the extension of public transport services near Papakura, and the lack of funding for a new cycle path, were signs of a lack of commitment.
Chris Darby supported the declaration but said the council still had a political muddle that it needed to sort.
Darby referred to a council in-house Emission Reduction Plan drawn up by management but which faced "political clay in the way."
"This call to arms is really important, but has got to be backed up with real political action from now on," said Darby.
The environmental group Forest and Bird Auckland had urged councillors to make the emergency declaration on Tuesday.
"In Auckland, we are already seeing increasingly severe droughts and extreme storms, which are caused by climate change," said its regional manager Nick Beveridge.