The 2021 Diplomatic Bluebook said, for the first time, that repeated intrusions by Chinese government ships into Japan's territorial waters near the Senkaku Islands in the southernmost Japan prefecture of Okinawa are a violation of international law. China claims the islands as its own, calling them Diaoyu.

The report said that China's covert military expansion and increasing unilateral actions to change the status quo in the East China Sea and the South China Sea raise strong security concerns for Japan, the region, and the world.

In its report, Japan calls ties with China one of the most important bilateral relationships, expresses concern over several of China’s internal issues, and criticizes China’s expanded maritime activities in the East China Sea.

The report expresses serious concerns over China's new coast guard law, which took effect in February.