reported, adding that a group of China Marine Surveillance (CMS) ships were patrolling the same area.
"They were suspected of illegal fishing within China's territorial waters, according to the Xinhua reporter on board the CMS ship," the Xinhua report said.
They were driven out of the waters at about 10am by two CMS ships -- the Haijian 262 and the Haijian 263.
"The CMS fleet, composed of three ships, with the other being the Haijian 83, and a Haijian B-7103 helicopter. The fleet is conducting regular patrols of the Xisha Islands, which are now administered by Sansha City, which was set up in July last year," the report said.
The incident comes a day after an official said China will send a team at an "appropriate time" to survey the Diaoyu Islands; China is also locked in a diplomatic tussle with Japan over disputed islands in the East China Sea, which Tokyo calls Senkaku islands.
Li Pengde, vice director of China's mapping agency, told China Central Television (CCTV) that surveying by land would allow the mapping of caves and other features not visible from the air.
"My hope is that we can get under way under conditions where the situation is relatively good and the survey team's physical safety can be assured," Li said.
In December, Vietnam had alleged that two Chinese fishing vessels cut cables of a Vietnamese vessel doing seismic oil exploration work in the South China Sea.
Under new unilateral regulations introduced last year, China had authorised its police to board foreign ships found patrolling or fishing in disputed waters.
State-run CCTV said CMS ships completed a nine-day patrol of the Yongle Archipelago of the Xisha Islands on Wednesday morning.
According to the report, security personnel landed on nine islands of the Yongle Archipelago and a helicopter took aerial photos.
Tensions in region have risen since China began asserting territorial claims over South China Sea since last year countering the claims of Philippines, Vietnam, Brunei and Malaysia over a host of uninhabited islands.
The seas around them are said to be rich in natural resources.