Japan's foreign ministry said on Wednesday it has lodged a diplomatic protest to China for the activities of Chinese ocean research ship "Xiangyanghong 18" within Japan's exclusive economic zone in the East China Sea.

Japan Coast Guard spotted the ship extending a wire-like object into the ocean about 129 kilometres northeast of Taisho island earlier in the day, the ministry said in a statement.

China's research activities without Japan's consent would be "extremely regrettable", it added.

Taisho is one of the disputed islands in the East China Sea which Japan controls and calls the Senkaku Islands. On Tuesday, Chinese and Japanese coast guard ships faced off in the waters around the islands. (Reporting by Kantaro Komiya; Editing by Christopher Cushing)