Kina sendte torsdag 11 marinefartøy til området hvor tre omstridte øyer ligger. Kina viste til at sivile kinesiske fartøy var blitt trakassert.
The exercises are aimed at «sharpening response to emergencies in missions to safeguard territorial sovereignty», state-run Xinhua news agency said.
They involve 11 ships and eight aircraft, including vessels from marine surveillance and fisheries agencies.
The agencies’ ships had been «harassed» while in disputed waters, it said.
China said the exercises would take place on Friday, but gave no details of the location in the East China Sea.
State-run CCTV showed members of the Chinese military, as well as footage of a frigate, fighter jets and helicopters.
China, Japan and Taiwan all claim the islands, called Senkaku in Japan and Diaoyu in China. Japan controls the islands, which lie south of Okinawa and north of Taiwan.
It is unlikely the 11 Chinese ships will try to enter Japanese-controlled waters, but if they did it would be a major escalation of the dispute – from one involving civilian vessels to ones explicitly involving military ships and aircraft, says the BBC’s Rupert Wingfield-Hayes in Tokyo.
The US has called for cooler heads to prevail in the dispute, which has rumbled on for years. US Deputy Secretary of State William Burns visited both Tokyo and Beijing this week for talks.
But Japanese media reports say Japan and the US are planning a joint military exercise in coming weeks that will include retaking a remote island.