Five Chinese naval ships, including a guided-missile destroyer, were spotted Friday morning near the Chunxiao gas field in the East China Sea, where Japan and China have a dispute over demarcation, the Maritime Self-Defense Force said.

An MSDF P-3C patrol plane spotted the five vessels around 9 a.m. about 290 km northwest of Kume Island, Okinawa Prefecture.

It is the first time Japan has spotted Chinese warships near the gas field, although its research ships have often been sighted in those waters, the MSDF said. The ships' mission was unknown.