China's efforts to protect its submarine gateway to the South China Sea could broaden from standoffs with U.S. military planes to announcing an air defense identification zone, according to two retired People's Liberation Army officers.

China could seek to restrict the air space around Hainan Island as the United States routinely runs surveillance flights in the area, retired Col. Yue Gang said. The move would mirror an ADIZ China set up in November over portions of the East China Sea disputed with Japan.

"Although it's premature to set up an air zone over the entire South China Sea at this moment, it makes sense to build a partial zone covering the waters near Hainan, where China's biggest nuclear submarine base is located," Yue said.