Japan's campaign to accuse Chinese radars of "locking onto" a Japanese warship is more like a "political drama" to hype the "China threat" and will risk greater tension over the Diaoyu Islands dispute, experts said.

Observers warned that the hyped "lock-on incident" serves as part of Tokyo's excuse for military expansion and lifting legislative limitations on the country's armed forces.

Japanese Prime Minister Shinzo Abe condemned China on Wednesday after his defense minister Itsunori Onodera claimed on Tuesday that a Chinese navy vessel locked its fire-control radar on a Japanese destroyer in the East China Sea in late January.

Abe called the incident a "dangerous" act that could have led to a "contingency", Japan's Kyodo News Agency reported.

Beijing has not officially confirmed the incident. Ties were strained after the Japanese government in September illegally "purchased" part of the Diaoyu Islands, which have belonged to China for centuries.

Jiang Xinfeng, an expert on Japanese studies at the PLA Academy of Military Sciences, said a radar's "locking on" is a common and constant reconnaissance practice in regular missions, and the other side usually reciprocates.

"However, Japan in recent years has ramped up reconnaissance on Chinese vessels and aircraft, and Japanese media prefer playing up regular operations by the Chinese side," Jiang said.

A further deterioration of China-Japan ties is actually unfavorable for Japan, and is also not expected by Washington, Jiang said.

The hawkish elite within Japan have been trying to shape public opinion and utilize public fears by hyping the "worsening security circumstances", said Yang Bojiang, a researcher on Japanese studies at Chinese Academy of Social Sciences.

This year has witnessed Japan's first hike in its defense budget in 11 years with more arms purchase orders and the expansion of Self-Defense Forces staff.

Japan will not cut its defense budget in the upcoming years, Yang said.

A media frenzy on topics like territorial disputes and missile launches prevails in Japan. Yang said the right-wing tendency should be given "due alert" and the country's policies are moving to the right.

Reports of the incident have arrived in the wake of Japan's ruling coalition New Komeito party's leader Natsuo Yamaguchi's late January visit to China to warm up ties, said Hu Lingyuan, a professor on Japanese studies at Fudan University in Shanghai.

"Although the Shinzo Abe cabinet chose a temporary friendly posture for thawing ties, it is still hyping the 'China threat'," Hu said.

Tokyo has repeatedly resorted to so-called "emergencies in the neighborhood" as excuses for military expansion, and hyping the "China threat" is part of its plan, observers said.

The Abe cabinet on Jan 25 decided to review the current National Defense Program Guidelines before the year-end.

Tokyo cited Pyongyang's recent rocket launch and China's patrols in the waters off the Diaoyu Islands as factors requiring the review of the current guidelines, which were compiled by the ousted Democratic Party of Japan in 2010, Japan's NHK Television said.

"With the aid of such 'incidents', Tokyo is seeking to bluff the international community by depicting China as a 'troublemaker in the region'," Hu added.

Japan has ramped up measures to monitor and track Chinese vessels around the Diaoyu Islands, and scrambled F-15 fighter jets to follow patrolling China Marine Surveillance aircraft above the East China Sea.

Chinese Ambassador to Japan Cheng Yonghua on Tuesday rejected Tokyo's protests of Chinese patrol ships sailing in the waters off the Diaoyu Islands, and Cheng required Japan not to interfere with regular patrols by Chinese vessels.

Washington is "concerned about" the reported lock-on incident, said Victoria Nuland, spokeswoman of the US Department of State on Tuesday.

"I will say that with regard to the reports of this particular lock-on incident, actions such as this escalate tensions and increase the risk of an incident or a miscalculation, and they could undermine peace, stability and economic growth in this vital region," Nuland said.