Beijing has denied that the unidentified submarine that entered Japanese waters recently was Chinese. It has also lodged a formal complaint with Japan over the incident and the subsequent implications by Japanese media that the sub was Chinese. From The Japan Times:
The Chinese Foreign Ministry contacted the Japanese Embassy on Monday evening denying the possibility that the submarine was Chinese and describing the reports as false and regrettable, Foreign Ministry Deputy Press Secretary Yasuhisa Kawamura said.
The Maritime Self-Defense Force stopped looking for the submarine Tuesday afternoon.
Defense Minister Yoshimasa Hayashi said at a separate news conference there was no information that would help pin down the nationality of the vessel.