IMMIGRATION officials have conceded a massive overrun of asylum seekers arriving by boat since the federal budget, but have refused to be drawn on how much this will cost.

Immigration officials were grilled at parliamentary hearings yesterday about the surge in arrivals but deflected the cost to the budget, which Labor brought down with only a paper-thin surplus.

The weekend arrival of almost 500 asylum seekers on five boats underlined the pressure on border controls - almost 8000 people have arrived by boat since July.

Labor's revised Pacific Solution in Nauru and Papua New Guinea will accommodate about 2100 people, far fewer than the number who have arrived since August 13 when the policy was embraced.

Home Affairs Minister Jason Clare said people smugglers were making more money than some drug smugglers and they would fight to keep making money. He said people smugglers earned more than $1 million a boat and sometimes up to $2 million.

Immigration Minister Chris Bowen denied offshore processing on Nauru has failed to deter arrivals. ''There is wide awareness now of our new policies and that they are being noted, however, as I've consistently said, we have a very significant challenge in that we are tackling the lies and the spin of people smugglers,'' Mr Bowen told ABC radio.

Immigration Department chief Martin Bowles said the number of asylum seekers was higher than expected.