Beijing Capital Airport, already China's busiest, will open Terminal Three in late February ahead of this year's Beijing Olympics, but the city is already looking further ahead.

'According to evidence from many quarters, building a brand new airport will be quite hard,' Yang Guoqing, deputy head of the civil aviation regulator, told a news conference.

'Even before we start preparatory work, there's a whole load of things to be done. We have already submitted a report to related state organs, and we hope they can organise discussions on the site of the new airport,' he added.

When Beijing's new terminal, designed by British architect Norman Foster, comes on line, capacity will rise to 76 million, compared with the 52 million who used the saturated existing facilities last year.

Air travel in China is thriving due to roaring economic growth. Some 200 million people are expected to take to the skies this year, around one tenth more than in 2007, which has helped fuel a national airport building boom.

Mr Yang pointed out that Shanghai already had two major airports, and cities such as New York had three or more.

'What role would a second airport in Beijing have? Will it be just an auxiliary airport?' he said. 'These issues all need study.'

Mr Yang said work to choose a location had begun, but would not be drawn on where the airport would be. State media have speculated that southeast of Beijing is the likeliest place.

Beijing is hemmed in by mountains on the north, surrounded by military airfields whose airspace is carefully guarded, and there is another major airport in the nearby city of Tianjin, all of which complicated the decision, he added.

'We have to make sure a new airport does not clash with the existing Capital airport or Tianjin airport,' Mr Yang said.

But he poured water on the idea of further expansion at Beijing's other airport, at Nanyuan in the south of the capital and currently only used by an arm of Shanghai Airlines for domestic flights.

'It's still technically a military airport,' he said. 'If more airlines come in, its definition will have to be changed to that of a civil airport, and lots of coordination would have to be done. And we haven't done that.' -- REUTERS