A former National immigration minister has urged Cabinet to dump plans to detain potential boat people, warning the Government is headed down a dangerous path.

In a letter to ministers, Aussie Malcolm, who is now an immigration consultant, has told the Government there will be "no winners and ongoing problems for everyone" from legislation currently making its way through Parliament.

It will enable the Government to detain for up to six months any asylum seekers who arrive as part of a "mass arrival" of more than 10 people. Depending on their risk they would be detained at a correctional facility, army base or at the refugee centre in Mangere.

A select committee has considered the bill and all but one of 44 submissions opposed it. Labour and the Greens have written scathing criticism of the legislation which they say is unnecessary and breaches fundamental human rights.

The issue of asylum seekers has become a political football in Australian where its government has faced riots and suicides in its detention centres and boat people dying after the sinking of their ships.

Malcolm urged National to accept an offer from Labour for cross-party consensus on the issue, saying Australia was evidence of what happened when political parties didn't agree on the issue.

"Australia and New Zealand have marched to the beat of different drums on refugee and asylum seeker issues for many years and the evidence is we are the ones who have got it right."

National would be blamed "for years to come" for any problems with asylum seekers.

Experts were ready to help National with a co-operative effort, he said.

Labour's immigration spokeswoman Darien Fenton said the Government was wasting Parliament's time and money on a threat that didn't exist because a boat had never reached New Zealand.

Immigration Minister Nathan Guy acknowledged submissions were almost entirely against the bill but said he wasn't prepared to water it down.

"We need to use this legislation to manage a potential mass arrival and also send a strong message that this is about dissuading and deterring those that want to come to New Zealand and see us as a bit of a soft touch."

The risk of boat people reaching New Zealand was real after a steel-hulled vessel made it to Canada from Sri Lanka in 2010, he said.

However, the Greens say that freighter was funded to the tune of millions by a large wealthy ethnic community. Such a wealthy community did not exist in New Zealand and the waters around the country were too treacherous, they said.

- © Fairfax NZ News