Acting Prime Minister Kelvin Davis has concerns for the safety of boat people trying to cross the perilous Tasman Sea to make it to New Zealand.

"There is the Tasman Sea to be crossed and it's a few thousand kilometres of some of the roughest water in the world. It is a situation though [where] we have concerns for anyone who tries to get here by way of sea."

His comments follow a report that Australia's Operation Sovereign Borders intercepted four boats, carrying 164 people, which were trying to make it New Zealand, according to Australia's Courier-Mail.

It suggested people smugglers were trying to take advantage of New Zealand's more open stance, given Prime Minister Jacinda Ardern's offer to take 150 refugees from Manus Island and her strong comments on Australia's handling of the situation.

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Speaking to media this morning, Davis did not want to speculate on the scenario of boat people arriving in New Zealand.

"We're going to have to cross that bridge when we come to that, but right now the offer is for 150 people from Manus Island to come to New Zealand."

He did not think New Zealand was being soft.

"It's not going to be easy crossing the Tasman Sea, so I don't think we are an easy target."

National Party leader Bill English accused Arden of "making a bit of a show of putting pressure on Australia over Manus Island, knowing that Australia won't take up the offer".

He said the story of the boats heading to New Zealand was a sign of the "cost" of Ardern's position.

"We rely on the cooperation with Australia to ensure people don't head to New Zealand in these boats ... It's the Australian authorities that see them and turn them around."

It is not known when the boats were intercepted or what country they started from but the Courier-Mail reported that they were turned or towed back to near Indonesian waters.

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Green Party foreign affairs spokeswoman Golriz Ghahraman said New Zealand should be proud of its more humane approach and should not be afraid of boat people trying to reach our shores.

"We are more open and it's something we can be really proud of because we are upholding our values and our law.

"People have a right to escape war and torture. We will process them if they are being persecuted and we will give asylum [if they are found to be genuine refugees]."

Asked about a scenario where people were trying to get to New Zealand and their boat overturned in the Tasman Sea, she said: "That would be tragic, but the answer to that isn't, 'let's keep them in a situation where they are facing torture or war'.

"There's all sorts of things you can do to keep people safe. The answer isn't to keep them from escaping torture."

She accused Australia of "scaremongering".

"The timing aligns with the Manus issue and the fact that we've made Australia look really bad. Australia is trying to divert attention away from what it's doing on Manus Island, which is essentially torturing people.

"Today, it's 'boats are coming to New Zealand, look out' ... whether or not it's true, it's not something we should be afraid of. We've always just processed people."

Davis did not want to say whether any boat people arriving in New Zealand would be processed.

"There's a lot of water to be sailed over before we get to that situation."

Asked if Australia was pushing back against Ardern's stance, he said: "Quite possibly, but we're not responsible for Australia and the decisions they make."

Ardern has previously said that New Zealand was a "very difficult" target for people-smugglers.​