Prime Minister Jacinda Ardern tried to "hitch a ride" to Nauru with the Australian contingent rather than have a New Zealand Air Force plane make a round-trip flight to pick her up at a cost to taxpayers of at least $80,000.

Speaking to reporters today, Ardern said she was stuck between a rock and a hard place in deciding to attend the Pacific Islands Forum in Nauru for one day on Wednesday.

An Air Force 757 took Foreign Affairs Minister Winston Peters and the rest of the New Zealand contingent on Monday but will return to New Zealand to collect Ardern and fly her there for the leaders' retreat on Wednesday.

"Damned if I did and damned if I didn't. I weighed this up. I even went to the extent of checking whether or not I could hitch a ride with Australia. We checked multiple options to try to find alternate ways for me to get there.

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"The option was go for a short time or not go at all. If I didn't go, I imagine there would have been equal criticism."

Ardern said if she had chosen not to go, she would have been the first prime minister outside an election cycle that would not have gone since 1971.

Ardern was not able to go to Nauru on Monday because of the length of time she would have been away from her young daughter, who is not yet immune to conditions on Nauru and therefore unable to accompany her mother.

National leader Simon Bridges said the public would judge whether the Prime Minister's trip was a good use of taxpayers' money.

"New Zealanders will judge this and there will be a wide range of views. They know MPs have to justify their expenses. I've had to."

Ardern said yesterday that the flying hours of the Air Force 757 were budgeted for and would be used regardless of whether she took the 11-hour round trip. The plane was unable to remain on the tarmac on Nauru and would have had to have flown to the Marshall Islands, and hour away, to park.