New Zealand lengthening detention for maritime arrivals

New Zealand's immigration minister insists he is "absolutely not" following Australia's path to remove legal rights of asylum seekers after announcing a law to lengthen detention during processing.

The government is introducing a "mass arrivals" bill that will allow asylum seekers to be detained for up to 28 days, should a ship with those seeking refuge land in the country.

Under current law, authorities have the power to detain asylum seekers for four days.

Immigration Minister Michael Wood admitted the likelihood of an arrival was low but he had "credible information and intelligence that NZ continues to be a destination of interest for people smugglers".

"You want to have your legislation ready in the event that something happens. You don't want to have to scramble," he said in Wellington on Tuesday.

Mr Wood cited the MV Sun Sea, a cargo ship carrying almost 500 Tamils seeking asylum from Sri Lanka, which arrived in Canada in 2010, as a possible precedent for NZ.

Mr Wood argued the law tweak was recommended by officials as necessary to safeguard rights during a "high impact event", allowing asylum seekers time to seek legal representation.

"That we have a credible, reasonable rights compliant framework that enables us to handle what would be a very challenging situation as smoothly as possible," he said.

The government believes in practice, it would only detain people deemed to be at risk to the community or those it believes may abscond.

However, the Greens have accused the Labour government of playing cynical politics.

"The government is today extending the power to detain them without charge or trial, without the right to be heard, rather than honour our commitment to uphold people's basic rights to safety and fairness," refugee spokeswoman Golriz Ghahraman said.

"The legislation is especially upsetting because it is unnecessary.

"We are not facing large numbers of boats carrying asylum seekers entering New Zealand waters. It is a conscious political choice to go down this route for no reason, and goes against who we are."

Mr Wood denied Australian-ising New Zealand's system of processing asylum claims, or that Australia had leaned on the government.

"New Zealand's approach has always been to support the human rights of people who arrive in New Zealand under the range of circumstances," he said.

"The main driver behind this change ... is about ensuring that people who might arrive at the situation, very vulnerable people, are able to have legal representation in the courts."