Wellington: New Zealand promised its public sector would become carbon neutral by 2025 as it declared a climate emergency on Wednesday, a symbolic move that critics said needed to be backed with greater actions to reduce emissions.

Prime Minister Jacinda Ardern said the climate emergency declaration was based on the Intergovernmental Panel on Climate Change's findings that to avoid more than 1.5 degree Celsius rise in global warming, emissions would need to fall by around 45% from 2010 levels by 2023 and reach zero by around 2050.

"This declaration is an acknowledgement of the next generation. An acknowledgement of the burden that they will carry if we do not get this right and do not take action now," Ardern told lawmakers in parliament.

After an hour-long debate, a majority of parliamentarians voted in favour of the declaration. The main opposition National Party voted against it saying it was nothing but "virtue signalling".

New Zealand joins 32 other countries including Japan, Canada, France and Britain that have declared a climate emergency.

Ardern, who returned to power in October delivering the biggest election victory for her centre-left Labour Party in half a century, has called climate change the "nuclear free moment of our generation".

In her first term she passed a Zero Carbon Bill, which sets the framework for net zero emissions by 2050 with an exemption for farming, and banned new offshore oil and gas exploration.

Nearly half of New Zealand’s greenhouse gas emissions come from agriculture, mainly methane.

The government on Wednesday promised the public sector will achieve carbon neutrality by 2025. Government agencies would have to measure and report emissions and offset any they can't cut by 2025.

The programme will be backed by a NZ$200 million ($141 million) fund to finance replacing coal boilers and help purchase electric or hybrid vehicles, it said.

Greenpeace welcomed the declaration, but challenged the government to follow through with policy and action.

"For Jacinda Ardern's climate emergency declaration to be more than just words, that means tackling New Zealand’s largest source of climate pollution: agriculture," said Greenpeace agriculture and climate campaigner Kate Simcock.