China will remain on high alert over Huangyan Island after a group of Filipinos reportedly planned to sail to the island in the South China Sea, a spokesman said on Friday.

"Huangyan Island is part of China's territory," Foreign Ministry spokesman Hong Lei said at a regular news briefing in response to a journalist's question.

Media reports said the group, headed by a retired Filipino military officer, intended to travel to the island and plant a Philippine flag, before being barred from doing so by Philippine President Benigno Aquino III.

"We have taken note of the reports you have mentioned," Hong told a reporter, adding that the Chinese side will "remain on high alert over the island to prevent any provocative behavior.

"We also hope that the Philippine side will stop making irresponsible remarks and inciting radical behaviors," he said.

He also urged the Philippines to "come back to the right track of a diplomatic solution" to the ongoing dispute over the sovereignty of Huangyan Island and "send clear and consistent messages" on the matter.