Judith Collins has launched a stinging attack on Jacinda Ardern, saying the Prime Minister needs to understand our relationship with Australia isn't "student politics".

Ms Ardern has used stronger language to describe Australia's treatment of refugees, particularly those stranded on Papua New Guinea's Manus Island, than her predecessor Bill English.

"There is absolute need and there is harm being done," she said last weekend, and has made the refugee situation the focus of her initial discussions with Australian Prime Minister Malcolm Turnbull.

Appearing on The AM Show on Friday, Ms Collins said it was "unfortunate for the Prime Minister Jacinda Ardern to go charging in like she did and try and embarrass the Australians".

"This is a very complex issue, and there's more information coming out that's making it look even more complex. There's more information today out in the media around some of the people who are on this island."

Ms Collins didn't elaborate on what she's heard. It could be unconfirmed reports in Australian media that some of the asylum seekers have been luring underage girls into rented rooms in Lorengau, a small town on Manus Island, for sex.

"They've gone through a UN process now, but they certainly haven't had the sort of screening that New Zealand normally expects. We just want to be a little bit careful, see what else comes out."

She said Ms Ardern needed to "learn from Winston Peters that you actually do have to be a little bit more statesman-like when you're overseas and representing New Zealand".

"It's not student politics time. This is where she's going to have to step up a bit."

The offer to take some of the refugees off Australia's hands was originally made by the previous National-led Government.

Labour MP Phil Twyford, also appearing on The AM Show, said there was nothing wrong with Ms Ardern talking tough with our neighbours.

"She's confident the relationship is secure and strong enough…¦ that we can actually talk about, in a robust way, matter of principle."

He criticised the National Government's "don't rock the boat" approach to trans-Tasman relations.

"As a result, we got walked on time and time again… The Australians are family, and we can talk frankly and candidly with them."