Japan's coast guard says more Chinese government ships were spotted last year trying to approach Japanese fishing boats in the country's territorial waters off the Senkaku Islands in the East China Sea.

Japan Coast Guard officials say 18 cases of Chinese government vessels approaching Japanese boats were confirmed in 2021, up from eight cases in 2020.

Japan controls the islands. The Japanese government maintains that they are an inherent part of Japan's territory. China and Taiwan claim them.

The Japan Coast Guard also reported 34 cases of Chinese government vessels sailing into Japanese waters last year. That's up 10 from the previous year.

Chinese ships sailed within the contiguous zone outside Japan's territorial waters on 332 days in 2021, almost the same as the previous year's record of 333 days.

China is increasing its maritime activities. Last February, the country enacted a law allowing its coast guard to forcibly remove foreign ships that it says illegally enter the country's waters, and to use weapons against them if they do not comply with certain orders.

An expert on international maritime law says China's moves could further intensify.

Kobe University Professor Emeritus Sakamoto Shigeki says China intends to undermine Japan's effective control of the islands by cracking down on Japanese fishing boats.

The Japan Coast Guard is stepping up its vigilance. It plans to add 10 large patrol vessels to its fleet by fiscal 2025.