People smugglers will be patient before trying to ramp up their operations again, the military head of the Government's border protection operation has warned.

Since the implementation of Operation Sovereign Borders there has been a dramatic decrease in the number of asylum seekers attempting to reach Australia by boat.

The Commander of Operation Sovereign Borders, Lieutenant General Angus Campbell, told a Senate Estimates hearing he could not comment on the effect of changes in government policy.

However, he said the threat of people smugglers remained.

"They are indicating a degree of patience and a willingness to restart their business whenever they regard conditions as being favourable," he said.

Meanwhile, the Department of Immigration said it is not considering re-settling refugees from the Manus Island Detention Centre in Cambodia.

The Government recently signed a $40 million deal with Cambodia to re-settle refugees from Nauru.

Assistant Secretary Mark Cormack said there were no plans for asylum seekers on Manus Island to be part of that deal.

"Refugees are currently being settled in Nauru, being offered on a voluntary basis to accept settlement in Cambodia, and that's what we're working on at the moment," he said.

"The MOU [Memorandum of Understanding] with Cambodia has just recently been signed, and now we're working on the implementation of that, and at this stage that does not include PNG."