The Chinese military has been monitoring a US guided-missile cruiser that illegally entered Chinese waters near the Nansha Islands on Tuesday morning, a spokesman from the People's Liberation Army said.

"Without the approval of the Chinese government, the guided-missile cruiser USS Chancellorsville illegally entered the waters near the islands and reefs of China's Nansha Islands on Tuesday," Senior Colonel Tian Junli, spokesman for the PLA Southern Theater Command, said in a statement.

"The theater command has organized naval and air forces to track, monitor and warn it off," he said.

The spokesman said that the warship's move, which seriously infringed on China's sovereignty and security, is more "hard proof "that the United States is seeking maritime hegemony and militarizing the South China Sea.

The move fully demonstrates that the US is the true manufacturer of security risks in the region, he said.

Tian stressed that China has indisputable sovereignty over the South China Sea islands and their adjacent waters, warning that the troops of the theater command are always on high alert to resolutely safeguard China's sovereignty as well as peace and stability at sea.