China will send six more patrol vessels into the South China Sea during the next three to five years to curb illegal fishing in the region, an official told the International Herald Leader newspaper of the Xinhua News Agency on Friday.

"A patrol vessel with a water displacement of 2,500 tons is expected to be sent next year into the South China Sea, with five more 3,000-ton vessels expected to go in the next three to five years," the agriculture ministry official who is in charge of the administration of fishery in the South China Sea said.

Yuzheng 311, China's largest fishery administration vessel, is pictured as it arrives in the Xisha Islands in the South China Sea, March 17, 2009. [Xinhua]

The patrol vessels will carry helicopters for efficient sea supervision, the report said.

This is "in accordance with the need to curb growing illegal fishing activity and to protect China's rights and interests", the official said.

He, however, denied that the plan was a response to the country's recent disputes with its neighbors over sovereignty of the Nansha Islands in the South China Sea.

Last Tuesday, China's largest fishery patrol vessel, China Yuzheng 311, which was converted from a naval warship, was sent to the waters around the Nansha, Xisha and Zhongsha islands.

The Ministry of Foreign Affairs has repeatedly reaffirmed China's sovereignty over those islands during the previous fortnight.

Amid mounting tensions, Liu Jianchao, the Chinese ambassador to the Philippines, has called for both sides to calm down and resolve the issue diplomatically.

"A spat over the issue will lead to no favorable outcome for anyone," Liu said on Thursday.

On the Filipino side, government press secretary Cerge Remonde said the department of foreign affairs in Manila was "already using normal diplomatic channels to solve this diplomatically".

"While it is true that this is a cause for concern, let us not overreact," the Manila Times quoted him as saying, on Thursday.

Gilberto Teodoro, the defense secretary of the Philippines, also said he did not really think China's deployment of the Yuzheng 311 was "a big threat".

"There is yet no cause for alarm as sending patrol boats by different claimant nations into the areas that they claim is tolerated," the Philippines' Navy spokesman Colonel Edgardo Arevalo was quoted as saying by news agency AFP.

Chinese analysts have said that the Philippines should "face reality" and "return to talks" for a win-win solution to the dispute.

Professor Li Jie, a senior naval researcher at the Chinese Navy's Military Academy, said: "China has shown restraint by sending patrol vessels to carry out routine fishery supervision.

"It has never occupied any islands in the sovereignty of its neighboring countries in the South China Sea by force."

Song Xiaojun, a Beijing-based military expert, also said that China was trying to avoid a conflict with the Philippines by sending only fishery patrol vessels to the troubled waters.

The move to send fishery patrol vessels means Beijing is acting according to diplomatic principles, Song said, noting that it was only to protect China's rights in the sea.

Meanwhile, the Shanghai-based Oriental Morning Post said the South China Sea dispute has posed little threat to trade cooperation between the two Asian nations.