China's Defence Ministry on Thursday accused Japanese air force jets of locking their radars on to Chinese military aircraft, acting provocatively and endangering safety, after Japan said it is scrambling a record number of fighter jets.



China and Japan have long been mired in a territorial dispute over a group of tiny, uninhabited East China Sea islands, called the Senkaku in Japan and Diaoyu in China.



Patrol ships and fighter jets from Asia's two biggest economies have been shadowing each other on and off near the islets, raising fears that a confrontation could result in a clash.



In the six months ending in September, Japanese fighters scrambled to chase Chinese planes 407 times compared with 231 times in the same period last year, the Japanese Air Self-Defence Force said in mid-October, an increase of about three-quarters.



Chinese Defence Ministry spokesman Wu Qian said Chinese air force activities accorded with international law and norms, and that it was Japan which was increasing its monitoring and interfering in normal training exercises.



"What is more, when aircraft of the Japan Self-Defence Forces encounter Chinese aircraft, their radars light up, they let off infrared jamming projectiles and show other unprofessional, dangerous provocative behavior," Wu said at a monthly briefing.



"This endangers the safety Chinese aircraft and personnel and is the root of the China-Japan maritime and air problem."



China urges Japan to adopt a responsible attitude and prevent such incidents from happening, he added.



Japan worries that as China increases its control over the South China Sea, it is turning its attention to expanding its influence in the East China Sea and into the western Pacific.



China insists regular patrols in the region are its right and intended to protect national security and sovereignty.



Tokyo's support for a July ruling by an arbitration court in the Hague that invalidated China's sweeping claims in the disputed South China Sea, a case brought by the Philippines, has also angered Beijing.



China refuses to recognize that decision and says countries not directly involved in the disputes, namely the United States and Japan, should not get involved.



Japan is strengthening its ties in the region, in particular with the Philippines and Vietnam, which contest China's claims to parts of the sea, and it aims to help build the capacity of coastal states in the busy waterway.



Philippine President Rodrigo Duterte said on Thursday his country could join naval exercises with Japan.