Zhoushan Island is the principal and namesake island in the Zhoushan Islands, formerly romanized as the Chusan Islands, an archipelago administered by Zhoushan Prefecture in Zhejiang Province in the People's Republic of China. It is the province's largest island and 3rd-largest in mainland China after Hainan and Chongming. The island is the distriā¦Zhoushan Island is the principal and namesake island in the Zhoushan Islands, formerly romanized as the Chusan Islands, an archipelago administered by Zhoushan Prefecture in Zhejiang Province in the People's Republic of China. It is the province's largest island and 3rd-largest in mainland China after Hainan and Chongming. The island is the district seat of both Dinghai and Putuo. The island was the site of the first and second capture of Chusan during the First Opium War.