Japanese activists have swum ashore and raised flags on an island claimed by both Japan and China, fanning an escalating territorial dispute between the two countries.

Some 10 activists landed on Uotsuri, the largest island in a small archipelago known in Japan as the Senkaku Islands and in China as Diaoyu Islands. The uninhabited islands surrounded by rich fishing grounds are controlled by Japan but also claimed by China and Taiwan. Earlier, a group of 14 Hong Kong residents and mainland Chinese had traveled by boat to the islands, and some swam ashore. Japan arrested them on Wednesday for landing without authorization, then deported the group on Friday. Xinhua News Agency reported that many from China’s cities of Guangzhou, Shen Zhen and Qindao marched to protest Japanese activists’ arrival to the disputed islands.