Japan had announced that it would co-patrol the South China Sea along with the US. Photograph: (Reuters)
Beijing's threat comes after Tokyo announced its plans to up its operational activities on the disputed waters
China warned Japan that it will not "sit and watch" while Tokyo increases its operational activities and hold military drills along with the United States on the disputed waters.
The Chinese defence ministry told Tokyo not "to mess up the South China Sea situation and try to gain interests from the troubled waters".
"If Japan wants to conduct any joint patrol or joint exercises in waters administered by China, it is just like playing with fire, and the Chinese military will not sit and watch," ministry spokesman Yang Yujun told a regular press briefing.
Tension between China and Japan, long-time sparring partners, escalated again when 40 Chinese military aircraft including surveillance planes apparently entered Japanese airspace on Sunday (September 25). Tokyo responded by dispatching fighter jets to tackle the situation.
China had said they were conducting a "routine drill on the high seas".
Beijing's aggressive posturing comes after Tokyo's decision to increase its activities in the South China Sea.
China had earlier responded to Japan's plans by indicating they would station a heavier military apparatus on the hotly-disputed Spratly Islands.
Tokyo, a key US ally, is also strengthening defence ties with other countries in the disputed region. Japan and China are already at loggerheads over a longstanding territorial row in the East China Sea.
In recent months Japanese Prime Minister Shinzo Abe has criticised China for rejecting a July ruling by an international tribunal, which said Beijing's extensive claims to the waters had no legal basis.
That dispute relates to uninhabited islets controlled by Japan known as the Senkakus in Japanese and the Diaoyus in Chinese.
(WION with inputs from AFP)