Chinese trawlers are active in the South China Sea
One of China's largest fisheries patrol ships has arrived at the disputed Paracel Islands.
The move comes after China protested to Manila over new legislation proclaiming Philippine sovereignty over parts of the disputed Spratly islands.
Both the Paracels - known in China as Xisha - and the Spratlys are subject to overlapping claims.
Separately, China and the US were involved in naval skirmishes last week off the Chinese island of Hainan.
The China Daily said that the patrol ship, a retired Chinese navy rescue vessel, the China Yuzheng 311, set sail from Guangzhou last week and reached the Paracel island group during the weekend.
The official newspaper said the vessel was on a mission to strengthen fishery protection and maritime surveillance after an incident between Chinese vessels and a US navy ship a week ago.
Analysts believe the new patrols are also linked to the passage of a controversial law in the Philippines last week, which seeks to define that country's territorial waters.
Sea of claims
Analysts of the many competing claims to islands across the South China Seas say the issue that entangled US and China navy ships off Hainan is somewhat different to that surrounding the Paracel and Spratly island groups.
SOUTH CHINA SEA TENSIONS
Territorial claims from China, the Philippines, Taiwan, Brunei, Vietnam and Malaysia overlap in resource-rich sea
Hosts some of the world's busiest shipping lanes
China says the US was in its Exclusive Economic Zone - but the two sides disagree on what activities are allowed in an EEZ
The US-China confrontation appeared to occur in China's designated economic exclusion zone and the conflict was over what activities, specifically intelligence gathering, are or are not allowable within such zones.
Contesting claims over the Paracel and Spratly islands are more complex, analysts explained, because sovereignty has not been finally established.
China, the Philippines, Vietnam, Taiwan, Indonesia, Malaysia and Brunei all have overlapping claims to groups of the islands, which are believed to have large oil and gas reserves.
Last week the Philippines president, Gloria Macapagal-Arroyo, signed a law which put in writing the country's long-standing claim to what Manila calls the disputed Kalayaan island group and the Scarborough Shoal, prompting protests from Beijing.
Beijing called the law "illegal and invalid".
China also reaffirmed its claims, saying the ship would "protect fishing vessels around Nansha, Xisha and Zhongsha islands in China's southernmost maritime territory".
A few days before the Philippines passed its law, Malaysian Prime Minister Abdullah Badawi inspected Danwan Reef, part of the Spratly Islands, and claimed sovereignty over the reef and adjacent waters.