Supplied image of a boat carrying 66 asylum seeker

Supplied image of a boat carrying 66 asylum seeker Photo: Supplied

Unmanned aerial drone surveillance will form part of a Coalition government's measures to halt the flow of asylum seeker boats, defence spokesman Senator David Johnston has said.

He also suggested officers on Customs and Navy boats in remote international waters would be given the job of deciding whether asylum seekers were genuine.

Senator Johnston said on Thursday that the opposition would spend $1.5 billion on seven drones and aim to have them patrolling Australia's waters and international waters within four to five years.

He said that currently 90 per cent of asylum seekers intercepted at sea were taken to Christmas Island.

Senator Johnston was speaking after a boat carrying 66 asylum seekers arrived from Sri Lanka at the WA town of Geraldton on Tuesday, saying they were trying to get to New Zealand. The group will be taken to Christmas Island to assess their claims.

''Obviously given the threats at the moment and the fact that we've had a boat come all the way down to Geraldton, obviously seven might need to be rethought,'' Senator Johnston told the ABC.

''But they do have up to a 42-hour loitering or flying time, endurance time, such that it just gives us a huge capability.''

Senator Johnston said that once boats were detected, surface craft would be sent after them to intercept the boats and to turn them around where it was safe to do so, and with the co-operation of the countries they had left.

''Now we would anticipate intercepting them at a much earlier stage with this platform,'' he said.

''So we'd be much closer to both Indonesia and Sri Lanka in this particular instance, such that it would give us a greater opportunity to engage authorities and say look we've got this boat coming, it's not seaworthy, we're going to bring it back.''

Greens leader Christine Milne dismissed the drones plan as part of the ''weird and wonderful'' ideas floated before the federal election in September.

''We're going to see a lot of propositions either put out there or debated for base political reasons, not because they're ever likely to happen,'' Senator Milne said.

Independent MP Bob Katter also weighed into the debate on Thursday, saying Australian waters should be patrolled for asylum seekers by missile-equipped boats to help protect against any other potential threats.

Mr Katter said Australia doesn't have enough military and customs resources to patrol the massive coastline, and more boats were needed.

''We need 100 patrol boats, a bit bigger than the conventional patrol boats ... built to take six cruise missiles and have interception capacity,'' he said.

The missiles would purely be for defensive purposes, he said.

''Normally, they would operate just as a patrol boat.''

Katter's Australian Party suggested putting aside 10 per cent of customs duty to fund it.

Senator Johnston suggested that Navy and Customs officers could be responsible for determining whether people intercepted in boats were genuine refugees under a Coalition government.

He said: ''I think ultimately the interdiction crew that our patrol boats and our Customs boats would put on board would make an adjudication.

''Normally we would obviously, the interception takes place way out at sea, a long way from anywhere, normally we'd bring them to Christmas Island. That would probably be 90 per cent of the cases,'' he said.

Opposition Leader Tony Abbott and immigration spokesman Scott Morrison have consistently said that the Coalition would turn back boats when it was safe to do so as part of their border protection policy.

Earlier this month, Indonesian police senior commissioner Parsaoran Damanik, of Banten Police in West Java, attacked the tow-back plan, saying it would ''disadvantage'' Indonesia.

''Absolutely it's a disadvantage for us. [Our actions] are not only about protecting our country's interests but we're also protecting Australia's interests,'' he said.

He said that Australia's current policy of processing asylum seekers on Nauru or Manus Island was better because Indonesia could not handle more asylum seekers being returned.

''We could arrest around two groups of illegal migrants per week, but we cannot put the migrants into jail. [All we can do is] legally process the drivers, the smugglers, vehicle owners,'' he said.

The federal government is considering replacement options for its AP-3C Orion manned maritime surveillance aircraft.

Immigration Minister Brendan O'Connor said on Thursday that he had not yet received answers on why the asylum boat made it to the mainland, but that people should not be too concerned about such a ''rare occurrence''.

Mr O'Connor told ABC radio that he did not believe that the boat's captains had adopted a new strategy to reach Australian shores, but he would need to get this confirmed by the agency.

''I think this vessel is . . . an exceptional case. We'll examine the reasons this has occurred. We'll certainly explain that publicly once we've confirmed that.''

with AAP

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