Opposition immigration spokesman Scott Morrison says a coalition government would keep aspects of Kevin Rudd's hardline stance on asylum seekers.
But he's raised doubts about the prime minister's ability to implement the policy, which he says is light on detail.
He described it as "the blank cheque solution".
"Once again we have a prime minister making a big announcement but the detail and the operations and the costs are completely unknown," he told reporters on Saturday.
Mr Rudd announced on Friday that people who arrive by boat and without a visa will have no chance to settle in Australia.
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They will instead be sent to Papua New Guinea and settled there.
"The problem is not with the idea but with this government's inability to implement ideas," Mr Morrison said.
"The coalition sees some merit in these measures and they can certainly complement the measures that the coalition stands by...
"(But) of course you need to go the extra distance and turn boats back where it is safe to do so."
Mr Morrison said the Liberals welcomed PNG's preparedness to resettle people.
"That is certainly something we'd be seeking to take up from them, as well as the ability to expand the regional processing capacity on Manus Island."
But Mr Morrison warned the policy raised a number of legal issues and could be subject to a legal challenge either in Australia or PNG.
He also said there were practical challenges in implementing such a policy in PNG which could take years to resolve.
