A Chinese senior diplomat on Monday said the current China-Philippines relations are "at a crossroads" and urged Manila to act with caution and stop any unilateral actions that may complicate the situation.

Vice-Foreign Minister Chen Xiaodong made the remarks in a phone call with his counterpart Philippine Foreign Undersecretary Ma. Theresa Lazaro, two days after a supply vessel and two Coast Guard vessels of the Philippines intruded into the adjacent waters of Ren'ai Reef in Nansha Islands, in an attempt to send construction materials to the military vessel illegally grounded at Ren'ai Reef.

It seriously violates the Declaration on the Conduct of Parties in the South China Sea, and the Philippines' own commitments, Chen said, adding such move also infringes upon China's territorial sovereignty and maritime rights and interests, and undermines regional peace and stability.

Noting China has indisputable sovereignty over the Nansha Islands, including Ren'ai Reef and its adjacent waters, Chen said the root cause of escalation of the on-site situation is Manila's reneging on its promises and stirring up trouble.

"China once again urges Manila to earnestly return to the right track of dialogue and negotiation with Beijing to properly resolve differences," Chen said.

"The Philippines should earnestly attach importance to China's concerns and work with China to safeguard the overall interests of bilateral relations and peace and stability in the South China Sea," he added.

He vowed China will continue to take necessary measures in accordance with domestic and international laws to firmly safeguard its territorial sovereignty and maritime rights and interests.

Chen also expressed China's solemn position on the Philippines' advancement of legislation on the "Maritime Zones Act", which he said further enforces the illegal arbitral award on the South China Sea by domestic legislation.

He said the act also includes China's Huangyan Island, most islands and reefs of China's Nansha Islands, and their adjacent waters into the Philippine maritime zone.

"It will intensify and aggravate maritime disputes between the two countries," he warned, urging Manila to immediately stop the legislative process that undermines China's sovereignty.