Hainan Airlines Co Ltd, the fourth-largest carrier in China, said on Wednesday that it is purchasing 30 Boeing 787-9 jets to expand its international routes and tap the growing demand for overseas travel in China.

The total cost of the new jets, which will be delivered before 2021, is expected to be about $7.7 billion, based on catalog prices. The carrier, however, said that the total purchase price would be lower than the estimates as Boeing is offering it discounts. "The jet purchase will improve our capacity and competitiveness," Hainan Airlines said in a statement.

The Boeing 787-9 is a stretched version of Boeing's popular 787 jets that have carbon-composite fuselage and improved fuel efficiency. The long-range, mid-size widebody, twin-engine jet has a passenger capacity of 280.