China Coast Guard has tracked and monitored two Philippine supply vessels and two coast guard ships which, on Friday, entered waters near the Ren'ai Jiao of China's Nansha Islands without the permission of the Chinese government, a spokesman said on Friday.

The spokesman for the China Coast Guard said in a statement that the four Philippine vessels were warned by the China Coast Guard, which "effectively regulated" them in accordance with law.

"China has indisputable sovereignty over the Nansha Islands and their adjacent waters, including the Ren'ai Reef," said the statement, expressing firm opposition to the Philippine attempt to transport building materials to the warship that is "illegally stranded" in the Ren'ai Jiao.

The spokesman added that China Coast Guard will continue to carry out rights protection and law enforcement activities in waters under China's jurisdiction in accordance with law.