Jacinda Ardern's plane breaks down in Antarctica

Jacinda Ardern has arrived back in the country from Antarctica, but not on a New Zealand Hercules as was planned.

The prime minister has been in Scott Base this week, marking the 65th anniversary of the site.

She was originally scheduled to leave yesterday, but was unable to due to a mechanical problem with the NZ Air Force Hercules.

The plane broke down and was unable to make the journey back.

Instead an Italian C-130 Hercules returned Ardern and her entourage to Christchurch this afternoon.

A New Zealand Defence Force spokesperson blamed breakdown on the C-130H being on the ground in Antarctica for two days.

"Experience has shown that cold temperatures can cause the aircraft propeller seals to have issues on start-up due to congealing hydraulic fluid and seal rigidity.

"To mitigate this issue propeller heaters are used and a methodical pre-flight process is used to warm the aircraft to a suitable operating temperature."

The spokesperson said it was unfortunate these steps had not worked this time.

"The C130H will be repaired and is expected to return to New Zealand in the next few days."

This is the second travel issue the prime minister has had on her Antarctica trip - her original flight was turned around due to bad weather.

ACT party defence spokesperson James McDowall said the breakdown showed it was time New Zealand increased its defence spending.

He said New Zealand's planes were ancient and falling to bits because the government was underinvesting in defence.

"It's just not a good look. You can't go around borrowing everybody else's Air Force. We should really just have our own well equipped."

ACT said the country should follow the NATO target and methodology for defence - which would see an extra $7.5 billion spent on capital expenditure over the next four years.

New Zealand has ordered five new Super Hercules aircraft which should be in service by 2025.

Groundbreaking research

Ardern said seeing the research being carried out in Antarctica firsthand was "something else".

What they were researching was so critical, not just to New Zealand but to the world, she said, that "it's ground-breaking".

The government's job was to support them, and make sure their research was informing decision making, she said.

Ardern also addressed geopolitical tensions in Antarctica.

She said in recent times they have seen some of the tensions that are being seen in other parts of the world also playing out in Antarctica.

She said New Zealand's position was "consistent and remains unchanged".

Regardless of what was going on globally, New Zealand's focus was to ensure Antarctica was "a place that is peaceful and secure, that is environmentally protected and that is a sound platform for people to safely engage in scientific research."

Ardern said New Zealand needed to maintain its efforts in international forums to protect the things it has always valued in Antarctica.

Electorate office vandalism

Her return also follows a vandalism attack which occurred at her electoral office yesterday morning.

Yesterday from Scott's Base Jacinda Ardern said she had seen some fairly "consistent" vandalism activity to electorate offices over the last few years.

She said she could not say whether they would become "more or less frequent in the lead-up to elections".

But regardless of the time of year "it's not okay," she said.

Her number one concern is for the safety of her staff.

They deserve "a safe place to work", she said.

Ardern said she was thankful to hear none of her staff were present at the time the vandalism occurred.

A 57-year-old woman at a Coatesville address was arrested in relation to the incident.