Japan has released a Chinese fishing boat captain whose arrest two weeks ago led to a major row with Beijing.
Japan had accused Zhan Qixiong of deliberately ramming two patrol vessels near disputed islands in the East China Sea, the BBC reports.
China said his detention was "illegal and invalid", and was sending a plane to bring him home.
The release came after four Japanese men were detained in China on suspicion of illegally filming in a military area.
A Japanese foreign ministry spokesman said its embassy in Beijing had received confirmation that the four were being held, but he said he did not want to speculate whether it was linked to Japan's detention of a Chinese fishing boat captain.
Officials said the four men were employees of a Japanese construction company who were in China to bid for a project to dispose of chemical weapons from World War II.
At a news conference, prosecutors in Naha, Okinawa, said Mr Zhan was just a fishing boat captain and had no criminal record in Japan.