China issued a strongly-worded protest and registered its opposition to the Philippines carrying out repairs to an illegally grounded warship near the Ren'ai Reef in the South China Sea, saying such a move proves the country is the real trouble-maker in the region.

View of part of the Xisha Islands in the South China Sea, 25 November 2011. [Photo/IC]

Manila grounded a warship near the reef in 1999 and has since rebuffed Beijing's demands to retrieve it.

Two Filipino officers told Reuters that the Philippine navy is reinforcing the hull and deck of the ship and work is due to be completed by year's end.

Philippine Foreign Ministry spokesman Charles Jose said repairs and maintenance of existing facilities are allowed ... especially if such work is for the safety of personnel and navigation, according to the news agency.

China has indisputable sovereignty over the Nansha Islands and adjacent waters, including the Ren'ai Reef, Foreign Ministry spokeswoman Hua Chunying said.

Hua reiterated China's resolution to safeguard its national territorial sovereignty as well as maritime rights and interests.

"We urge the Philippines to stop illegal activities and keep its promise to drag the ship away," she said, adding that China reserves the right to take further measures.

Hua pointed out that although the Philippines had promised many times to retrieve the ship it has attempted to permanently occupy the reef through maintenance work.

"The Philippines has lost its credit in the international community by eating its own words, and its activities have revealed its hypocrisy. This, again, proves that the country is the real trouble-maker and rule-breaker in the region," she said.