Marine surveillance ship Haijian 75 [File photo]

Two Chinese China Marine Surveillanceships returned to south China's city of Guangzhou on Tuesday after finishing patrols in the South China Sea, the State Oceanic Administration said.

The Haijian 167 and Haijian 75 completed patrols in waters surrounding the Xisha and Nansha Islands in 12 days, covering a distance of more than 4,000 nautical miles.

During the patrols, the two ships stopped foreign vessels committing illegal acts in China's territorial waters and effectively safeguarded China's marine interests, the administration said.