The People's Liberation Army's Southern Theater Command mobilized its air and naval forces on Wednesday to monitor the unlawful entry of a United States warship into China's territorial waters and warned it off, the command's spokesman said.

"USS Milius entered our territorial waters near the Xisha Islands in the South China Sea on Wednesday without the Chinese government's authorization. The move compromised the peace and stability in the region," Senior Colonel Tian Junli said in a statement.

"The Southern Theater Command will stay on high alert and take any necessary measures to safeguard national sovereignty and security as well as the peace and stability in the South China Sea," he said.

Based in Yokosuka in Japan, the Milius is an Arleigh Burke-class Aegis guided missile destroyer and is part of the US Seventh Fleet.