Prime Minister Jacinda Ardern has fired back at criticism from National and Act that the Government is not spending enough on defence - pointing out she has increased defence spending to levels National and Act never achieved in office.

National and Act have publicly floated the idea of lifting defence spending, with Act challenging the Government to outline a pathway of lifting defence spending to 2 per cent of GDP, often seen as an international benchmark.

In a statement to the Herald, Ardern said the Government has "significantly increased our investment in defence spending since taking office in 2017".

Ardern noted defence spending was ahead of some European and Nato countries, and was ahead of Canada, a Five Eyes intelligence partner.

She said spending on the military had "increased from 1.15 per cent of GDP in 2017 to 1.54 per cent of GDP in 2020, putting us ahead of the likes of Canada".

Canada spends 1.42 per cent of its GDP on defence, the Netherlands and Denmark spend 1.44 per cent and Sweden, which is not in Nato, spends 1.22 per cent.

Figures from the World Bank show defence spending fell to 1.11 per cent of GDP in 2011, the end of National's first term, the lowest in recent times. This increased to 1.15 per cent by 2017, when the current Government took office. It then increased the level of defence spending to 1.54 per cent.

"This increase in investment was necessary as the previous National government deferred investment in new planes and boats critical to supporting disaster relief at home and in the region," Ardern said.
"Our defence force plays a major role in the emergency response to climate-change-related extreme weather events such as cyclones and supporting security in the Pacific region, which is our foreign policy focus.
"This investment means we are better prepared for our climate and geo-political challenges," she said.

Much of the spend has gone on the purchase of new defence equipment. The Government has spent $4.5 billion on 12 defence capability projects, including the purchase of four new P-8A Poseidon aircraft, and replacing five of the C-130 Hercules arcraft with C-130J Super Hercules.

On Wednesday, National leader Christopher Luxon told the Herald that National was discussing policies that would lift defence spending.

"You've got to say 'how do we back up our words with actions?' and so getting back to making sure that we are carrying our responsibilities, that we have invested enough in defence, those are conversations that we have had in the party," Luxon said.

"We want to stand with our friends and our allies and our partners. That means we need to be able to back up our commitments and our words - we've got to make sure we are carrying out our piece of it - if that means looking at defence spending, so be it."