A Bahamas-registered maritime research vessel was sailing in Japan's exclusive economic zone near the disputed Senkaku Islands on Sunday with a wire lowered into the water, the Japan Coast Guard said.
The 11th Regional Coast Guard Headquarters in Naha, Okinawa Prefecture, urged the vessel, the Discoverer2, to desist as its activities contravened international treaties that require prior approval for research.
But the vessel responded in Chinese that the waters lie in China's EEZ and it had obtained approval from the Chinese government, according to the coast guard.
The vessel left Japan's EEZ at around 7:30 p.m., the coast guard said.
The vessel previously sailed in Japan's EEZ on June 17 and told a coast guard patrol ship that it belongs to a Chinese organization.