The Boeing Co. has finalized an order with Air China, the flag carrier of the People’s Republic of China, for 20 of the Renton-built Next-Generation 737-800 jetliners, according to a company press release.

Air China operates international and domestic passenger and cargo services. The carrier will use the airplanes to expand its domestic routes.

“Our long-standing and productive partnership with Air China goes back to the airline’s beginning and we’re proud to be part of their success,” said Jim Simon, vice president, China Sales, Boeing Commercial Airplanes. “Air China’s order reflects our solid partnership and the proven performance of the Next-Generation 737 in its fleet.”

Boeing announced in June that it will increase production rates on the Next-Generation 737 program to 35 airplanes per month in 2012. The rate increase will meet continued strong demand for the Next-Generation 737. The Next-Generation 737 family has more than 2,000 unfilled orders from customers around the world.