BEIJING - US-based Delta Air Lines bought 3.55 percent of shares of China Eastern Airlines worth $450 million on Monday.

The investment is part of a series of cooperation agreements signed by the two airlines, which both belong to SkyTeam Alliance.

"Delta's investment will help us promote mixed ownership and speed up our overseas expansion," said Liu Shaoyong, chairman of China Eastern Airlines.

China is the second-largest market for travel to the United States and is expected to take the lead in the next few years, according to Richard Anderson, CEO of Delta Air Lines.

The two airlines have signed codeshare agreements to operate 30 US domestic flights, 43 Chinese domestic flights and seven trans-Pacific flights.