China has said it will take forceful measures in response to any moves that challenge the country's sovereignty.
"We want to live in friendship with all countries including Japan, but we have to uphold our principles and bottom line," Chinese Vice Foreign Minister Zhang Zhijun told reporters Friday night.
Zhang said China pursues a policy of friendship and partnership with its neighbouring countries and stays committed to the path of peaceful development, reported People's Daily.
"However, should anyone want to challenge China's bottom line on the issue of sovereignty, China will have no alternative but to respond forcefully so as to remove disturbance and obstacles and move steadily on the path of peaceful development," he said.
Zhang said Japanese government's "purchase" of the Diaoyu Islands, which was announced Sep 10, constituted a grave violation of China's territorial sovereignty.
He said the move has caused "the most severe repercussions" on China-Japan relations since the two countries normalised diplomatic relations in 1972.
The Diaoyu Islands are part of China's territory in accordance with historical fact and law, Zhang said.
Japan has no right to buy or sell Chinese territory in any way and no transaction is allowed over even one inch of the Diaoyu Islands or anything on it, he said.