The China Coast Guard (CCG) on Monday issued stern warnings to the Philippines after detecting three Philippine vessels illegally intruding into waters adjacent to Ren'ai Jiao of China's Nansha Qundao to deliver materials to the Philippine warship illegally grounded on the reef.

"We would like to remind the Philippines once again that any form of infringement and provocation is futile. The Chinese Coast Guard is on full alert to resolutely safeguard China's territorial sovereignty and maritime rights and interests," Gan Yu, a spokesperson for the CCG, said on Monday.

According to Gan, three Philippine vessels dangerously approached and deliberately collided with Chinese ships that were sailing normally during their intrusion into Chinese waters.

He said the CCG warned the vessels and later intercepted, boarded and inspected them before driving them away, handling the matter in a professional manner in accordance with laws and regulations.