Quoting the State Oceanic Administration, Xinhua said that "on Friday the ships patrolled the territorial waters surrounding the Diaoyu Islands", which Japan claims as the Senkakus.
A report by Japan's Jiji agency said the ships entered waters around Uotsurijima, one of the five islands, at around 8.15 pm, staying there for two hours.
The incursion came as Japan's Prime Minister Shinzo Abe urged Chinese President Xi Jinping to reset dangerously frayed ties between Asia's two largest economies as they met on the sidelines of the G20 summit in Russia.
The islands - believed to harbour vast natural resources below their seabed - are seen as a potential flashpoint that some observers fear could lead to armed conflict between the Asian giants.