Japan has expressed serious concerns to China over a fresh drilling setup near a disputed gas field in the East China Sea
Tokyo said a vessel has been spotted drilling a platform on the Chinese side about 26 km from the disputed gas field.
BBC reports that Japan is concerned China would be able to tap gas from its side.
According to the report, the economic zones of both countries overlap at the gas field.
A co-operation agreement between the countries had broken down amid confrontation over disputed territory, report added.
Chief Cabinet Secretary Yoshihide Suga said Tokyo cannot accept China's unilateral development near the region, where Japan's and China's claims overlap.
China is yet to respond to Japan's concerns.
