Opposition leader Bill English is warning the Government to tread cautiously on its position on the humanitarian crisis on Manus Island, saying that New Zealand owes Australia for stopping boat people from reaching our shores.

About 400 refugees continue to refuse to leave a detention camp on the Papua New Guinean island since its closure two weeks ago, despite food, water and power being cut.

Some who have moved to alternative accommodation say that conditions there are worse than in the closed detention centre.

Last night Prime Minister Jacinda Ardern met her Australian counterpart Malcolm Turnbull, offering $3 million to help Papua New Guinea with the costs of keeping the asylum seekers, in conjunction with an agency such as the Red Cross.

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"New Zealand's offer [to take 150 refugees] remains on the table," she said from Manila, where she was attending the East Asia Summit.

"It remains on the table because the need remains. We believe we have a role to play as members of the international community but also as neighbours to Australia to offer our support in finding a resolution to this situation."

New Zealand officials would continue to work closely with Australian officials, which was "more progress that we have had on the offer in a number of years".

English questioned whether Ardern's offer was genuine, or simply putting on a show.

"To what extent is our Prime Minister making a showpiece out of this, knowing full well that the Australians are very unlikely to take up the offer because it would be a fundamental shift in their policy about boat people?

"The Australian system is what protects New Zealand from people arriving in boats. They're the ones who find the boats and then turn them around, if they are heading here. So we need to keep that in mind at a time when the New Zealand Government is criticising their policy."

Yesterday a media report in Australia suggested that Ardern's outspoken voice on Manus Island had stoked increased "chatter" among people-smugglers to try to get to New Zealand. It also reported that Australian authorities intercepted four boats, carrying 164 people, that were said to be bound for New Zealand - but did not shed light on when, or where they had come from.

Acting Prime Minister Kelvin Davis defended Ardern's persistence and forthright voice on the matter.

"Our Prime Minister has done us proud in the work she's done ... advocating for Manus Island. I think she's been very forceful and done us very proud in the discussions she's had with Australia."

He said that the $3 million could be used by Papua New Guinea to "alleviate some of the suffering on the island, specifically to assist those refugees on Manus Island".

"We'd work with the Papua New Guinea Government, if they want to draw down on that. We're working with Australia and hopefully we'll be able to sort the situation out."