The Philippines is in talks to possibly include Australia and Japan in planned joint South China Sea patrols with the United States, a senior diplomat said on Monday, in another sign of concern over Beijing's activities in the strategic waters.

"Meetings have already been set and probably we may have the Japanese and the Australians join in," Philippine Ambassador to the United States Jose Manuel Romualdez said.

"They would like to join in for joint patrols to make sure that there's the code of conduct and there's freedom of navigation," adding it was still "an idea under discussion."