He said while it was a difficult journey on treacherous water there was no question the landscape had changed with Australia now seen as "closed" and New Zealand as a possible alternative destination.
"I think they're now showing a renewed interest in other locations, and New Zealand is one of those."
Asylum seekers who arrive in large groups can be detained for up to six months under immigration laws changed by the Government last year.
Mr Key said he suspected the people smugglers understood the rules had tightened, but "they'll tell a very different message to those wanting to seek asylum".
"In reality these are desperate people who are looking for a better life, and so they'll want to believe the dream that somehow there would be easy access into New Zealand.
"In fact as we know, irrelevant of whether they're going to Australia, New Zealand or anywhere else, it's an extremely dangerous voyage. Many people have lost their lives, but all of that is underplayed."
Meanwhile a refugee centre for processing asylum seekers at Mangere in South Auckland was being improved, Mr Key said.