Boeing (BA) has signed a massive deal to sell 300 of its aircraft to China, making it its largest order from Chinese companies. The three buyers are China's ICBC Financial Leasing Company, China Aviation Supplies Holding Company and China Development Bank Leasing Company. Boeing also plans to build its first 737 aircraft plant in China to meet growing travel demands. This comes after rival Airbus Group (EADSY) signed a deal in July to build a second factory there. All of this as Chinese President Xi Jinping is visiting the United States this week. He landed in Seattle on Tuesday and is expected to visit Boeing today. The two companies will go head to head for plane orders in China, which is expected to beat the U.S. in two decades to be the world's biggest aircraft and travel market. TheStreet's U-Jin Lee reports in New York.