The debate over whether Sydney needs a second airport has been re-fuelled by the decision to award the G20 summit to Brisbane.

In outlining her reasons yesterday why Sydney was overlooked, the Prime Minister listed capacity problems at the Airport.

Ms Gillard says it is already under pressure and would not be able to cope with all the extra jumbos brought in by the world's leaders.

"Sydney Airport does have restrictions and a lot of pressure on it already," she said.

That has irked the State's Planning Minister Brad Hazzard.

"The Prime Minister and her senior ministers know that what they have done is unjustifiable so they're simply trying to highlight their argument that we need an immediate second airport," he said.

"Even they know we don't need an immediate second airport because their forecasts say nothing would be needed for at least 20 years," he said.

Sydney Airport chairman Max Moore-Wilton has also dismissed claims that another airport is needed.

"Nobody has 40 positions sitting around empty waiting to have them sit on the tarmac and we have plenty of capability as we did in the APEC for the planes to land and take off and they can park - I mean we've got Richmond Airport space down the road the only thing that occupies it basically most of the time is seagulls," he said.

But he is philosophical about the G20 decision and says Sydney cannot expect to get every big conference.

"These things are handed around," he said.