The Airport Authority will this year begin an engineering and environmental feasibility study for a third runway at Hong Kong International Airport, Financial Secretary John Tsang announced today.

Presenting his Budget in the Legislative Council, Mr Tsang noted that the airport is the world's fifth busiest in terms of international passenger throughput - and the busiest in terms of international cargo throughput.

Passenger and air cargo throughput reached new highs last year, with more than 47 million travellers passing through the airport and 3.74 million tonnes of air cargo handled, he said.

He noted that the Government announced last May that it would increase the capacity of the two existing runways progressively from 54 movements per hour to 58 movements per hour in 2009.

"With the support of the Airport Authority and the industry, we are confident that capacity of the existing runways can be gradually increased to 68 aircraft movements per hour by 2015," Mr Tsang said.

But, he stressed: "In the long run, it is important that the airport can further increase runway capacity to handle forecast growth in air traffic."

To meet the rising demand for container throughput, the Government has been identifying suitable locations for the development of Container Terminal 10, he added.

"The latest forecast shows that container throughput will continue to increase in the future after reaching a handling capacity of 24 million 20-foot equivalent units of containers last year."

He noted that two sites have been identified, at Northwest Lantau - which may require extensive reclamation and affect the ecological environment - and at Southwest Tsing Yi, which would require the relocation of the existing oil depot.

If the latter site was chosen, Mr Tsang noted, it could "achieve synergy with the container terminals in Kwai Chung and Tsing Yi".