"They must be stopped. New Zealand has played a role in trying to stop them."
New Zealand had worked with Australia for a number of years "to stop people at the source from risking their lives and trying to make that journey".
"We will continue to do so."
She said the reported "chatter" among people smugglers eager to try to get to New Zealand was nothing new.
"I've been given no indication that that chatter ever stopped. We know it has been an ongoing issue."
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 co-operation 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.
Ardern would not comment on whether the story was an indication that Australia might be pushing back against her comments about the situation on Manus Island, where over 400 refugees are facing a humanitarian crisis in an abandoned detention centre.
Yesterday she spoke with her Australian counterpart Malcolm Turnbull, though it was not a formal meeting.
"We've talked about the range of issues that lead to both the situation that we have on Manus and Nauru, and also what work we can do together to overall put an end to the risk that people are taking [by] boarding a boat."
Officials were continuing that conversation, she said.
Green Party foreign affairs spokeswoman Golriz Ghahraman said New Zealand 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."
Labour's deputy leader Kelvin Davis had concerns for the safety of boat people trying to cross the Tasman Sea.
"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."
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."
