Immigration Minister Tony Burke has revealed the population of asylum seekers on Christmas Island is falling for the first time under Labor, in a sign he says shows the Government's policies are working.

Mr Burke says there has been a significant decrease in the number of boat arrivals, with 1,585 asylum seekers arrived in Australia by boat in August, compared to 4,236 in August.

"It has also been true that now for the first time we are seeing the population on Christmas Island start to fall rather than rise," Mr Burke said.

"Anybody who thought there was going to be a capacity problem, the numbers now speak for themselves that there will not be.

"The impact of the policy and the communication of the policy is having the exact impact that we believed it would and we were determined that it would have."

so that asylum seekers who arrived by boat have no chance of being settled in Australia as refugees.

Under the policy, asylum seekers will be sent to Papua New Guinea's Manus Island for processing and resettled there if they are found to be genuine refugees.

A similar agreement has since also been signed with the government of Nauru.

The Government had said the deterrence effect of its policy would not be apparent immediately, instead, boat arrivals would slow once potential asylum seekers and people smugglers learnt of the policy.

Mr Burke also attacked the Coalition's plan to buy Indonesian boats that could potentially be used for asylum seeker voyages.

"It was one thing when I described the buy back the boats policy as the most absurd policy that I had seen, it is another thing with an independent fact check describes it as the most ridiculous of all the Coalition policies," he said of .

"There is some competition for that title, but buying back the boats wins it hands down."

, Opposition Leader Tony Abbott said the boat buyback plan was just one of a suite of measures that could be used to tackle people smuggling.

He conceded the Coalition may never buy an Indonesian boat.

"But if we did have the opportunity to pay someone a couple of thousand dollars to stop a boat from being launched, when, if that boat arrived in Australia, it would cost some $12 million per boat to deal with people, that would be a shrewd investment," Mr Abbott said.

"If we can interrupt a particular operation in this way that may well be a sensible thing to do," he added.