Air China signed an agreement Friday to buy 31 Boeing passenger and cargo planes from Boeing, subject to government approval, the Chinese flag carrier said.

Air China will purchase 20 Boeing 737-800 aircraft, two Boeing 747-8 aircraft, one Boeing 777-300ER aircraft and its unit Air China Cargo would buy eight Boeing 777 cargo planes, the airline said in a statement.

The total value of the deal is $5.2 billion at current Boeing list prices.

"The Boeing Company has granted to the company significant price concessions with regard to the Boeing Aircraft," Air China said.

Air China said the purchase would expand its overall fleet capacity by almost 19 percent and in particular strengthen the airline's market share in the international market.

"The company expects the Boeing Aircraft will deliver more cost-efficient performance and provide more comfortable services to passengers," it said.

Deliveries of the passenger planes are expected in 2014 and 2015, while Air China Cargo anticipated delivery of the 777 Freighters from 2013 to 2015.

Boeing spokesman Jim Proulx said the US aerospace giant would announce the order upon approval from Beijing.

"We look forward to working with Air China, a long-time valued customer, to obtain approval," he said in an email to AFP.

China's leading airline, which last year partnered with US JetBlue Airways, is seeking to expand its business in the United States.

Air China has been facing financial headwinds in recent months. According to the latest available earnings report, the carrier posted a 16 percent drop in third-quarter net profit from a year ago while sales edged up 2.2 percent.