China's Defence Ministry said on Thursday that Japan is "playing with fire" with plans to step up activity through joint training patrols with the US in the South China Sea and warned that it would not accept it happily.
During a visit to Washington, the defence minister of Japan said the nation will be strengthening its ties in the region, in particular with the Philippines and Vietnam, which contest China's claims to parts of the sea.
Japan will also aim to help in building the capacity of coastal states in the busy waterway.
China claims a vast part of the entire South China Sea and it has repeatedly asked the United States and its ally not to interfere there.
Yang Yujun, Chinese Defence Ministry spokesman asked about Japan's plans and said it had been constantly trying to stir things up in the disputed waters of the South China Sea for its own purposes.
"We must solemnly tell Japan this is a miscalculation. If Japan wants to have joint patrols or drills in waters under Chinese jurisdiction this really is playing with fire," Yang told Reuters.
"China's military will not sit idly by," he added. However, he denied elaborating any further.
The conflict between Japan and China has been rising due to "China's incursions into the waters of the Tokyo-controlled disputed islands". Since August 5, Japan has lodged at least 32 protests regarding 30 intrusions by Chinese vessels in the territorial waters.
But, China regards them as its own and rejects the view that it violates Japan's territorial waters.
Beijing claims almost all of the South China Sea where its territorial claims overlap in parts with Vietnam, the Philippines, Malaysia, Brunei and Taiwan.
An arbitral tribunal in The Hague ruled in July that China's vast territorial claims in the South China Sea have no legal basis. The court criticised Beijing's environmental destruction in the disputed area.
The ruling infuriated China and it refused to participate in the case. China denied to accept or recognise the tribunal's decision.
Apart from the South China Sea, Japan also has its own conflict with China over territories in the East China Sea.