Regular unleaded petrol costs more than $3 a litre in New Zealand, with some economists predicting it could reach $4 this year.

Prime Minister Jacinda Ardern said Russia's invasion of Ukraine has produced a "global energy crisis", and a "shock and a spike in prices at the pump felt by the whole world".

"The impact of the war sits on top of the pain already caused by the pandemic with global supply chain disruption and increases in consumer demand causing high levels of inflation in many countries," she said.

"We are in a wicked perfect storm, and it's a storm that's affecting people's lives."

New Zealanders are feeling the pinch more than most, currently enduring the highest CPI inflation levels since the early 1990s.

Ms Ardern's response is to cut petrol excise duty and road user charges for the next three months, which will reduce the cost of filling a 60 litre tank of petrol by around $NZ17 ($A16).

The government will fund the shortfall by moving $NZ350 million ($A327 million) from its unallocated COVID-19 response fund.

Energy Minister Megan Woods said she had spoken to leaders at petrol companies, seeking assurances they would pass on the discounts to consumers.

For three months beginning April 1, public transport will also be half price, which will cost approximately $NZ40 millon ($A37 million).

Australian Associated Press