Flagship carrier Air China said its board has approved an agreement to buy 15 Boeing 777 and 30 Boeing 737 aircraft in a deal that would be worth several billion dollars.

The catalogue price of the 45 planes is approximately 6.3 billion dollars but Air China said it expects Boeing to grant price concessions which will lower the overall cost, the carrier said in a statement late Tuesday.

The Boeing airplanes will be delivered between early 2011 and 2015, Air China said in the statement handed to the Shanghai Stock Exchange.

The airline said the purchase is expected to boost its carrying capacity by around 35 percent in terms of annual tonnage per kilometre from the 2007 level, according to the statement.

An official at the Beijing-based firm said the latest deal was separate from previous purchase agreements between Chinese carriers and Boeing.

"It's a new order," the official, who declined to be named, told AFP by phone.

Boeing signed agreements in November 2005 and April 2006 to supply Chinese airlines a total of 150 737 aircraft.