China Friday protested two Japanese local assembly members' landing on an isle of the Diaoyu Islands, saying the move seriously infringed China's territorial sovereignty.

"The Diaoyu Islands and its adjacent islets have been an integral part of the Chinese territory since ancient times," Foreign Ministry spokeswoman Jiang Yu reiterated Friday night.

According to reports, two members of the municipal assembly of Ishigaki, Okinawa Prefecture, landed on an islet of the Diaoyu Islands and stayed there for a while Friday morning.

Jiang said China has lodged a solemn representation and voiced strong opposition to the Japanese side.