The uninhabited islands -- known as the Diaoyu in China and Senkaku in Japan -- are claimed by Beijing but administered by Tokyo and are a frequent hotspot in bilateral tensions.
Liu Dejun, a spokesperson for Beijing's coast guard, said a Japanese fishing vessel had "illegally entered territorial waters" around the islands from Tuesday to Wednesday.
The coast guard "took necessary control measures in accordance with the law, warned (the ship) and expelled it", Liu said in an online statement.
"The Diaoyu and affiliated islands are China's inherent territory, and we urge the Japanese side to immediately stop all illegal activities in these waters," he said.
"Chinese coast guard ships will continue to carry out maritime rights protection and law enforcement activities... to safeguard national sovereignty, security and maritime rights and interests."
Japan's coast guard also said Thursday its patrol ships were monitoring four Chinese coast guard vessels near the islands.
It said that a Japanese fishing boat had been operating around 10 kilometres (6.2 miles) west of the largest landmass in the group as of 9 am (0100 GMT) on Wednesday.
Beijing has said several times this year that it has driven Japanese vessels away from the islands.
But Japanese officials have told AFP that Chinese authorities sometimes announce expulsions when none have occurred.
In recent months, China has pressed its sweeping territorial claims in the East and South China Seas more stridently.
It has notably reignited a years-long dispute with the Philippines over control of contested reefs and shoals in the latter's waterway.
Beijing on Monday also held military drills around Taiwan, the self-ruled island it claims as part of its territory and has refused to renounce using force to seize one day.
Perennial rivals in East Asia, China and Japan are major trade partners, but their relationship is complicated by Beijing's regional rise to prominence, Tokyo's alliances with Western nations and its imperial history.
Japan lodged protests after China tested an intercontinental ballistic missile in the Pacific Ocean last month, and Beijing banned Japanese seafood imports in retaliation for Tokyo's decision to release treated water from the disabled Fukushima nuclear plant into the ocean.
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