"We're aware a T-4 plane that belongs to the Air Self-Defense Force fell down immediately after taking off at Komaki Air Base" in central Japan, top government spokesman Yoshimasa Hayashi said.

"Details are being probed by the defence ministry," he told reporters.

The T-4 seats two and is a "domestically produced, highly reliable and maintainable training aircraft... used for all basic flight courses", according to the defence ministry website.

The aircraft was flying around Lake Iruka near Inuyama city north of Nagoya, according to media outlets including public broadcaster NHK.

"There is no sight of the plane yet. We've been told that an aerial survey by an Aichi region helicopter found a spot where oil was floating on the surface of the lake," local fire department official Hajime Nakamura told AFP.

He said his office had received unconfirmed information that there were two people on board but that they had not been able to independently verify this.

Aerial footage of the lake broadcast by NHK showed an oil sheen on its surface, dotted with what appeared to be various pieces of debris.

Just after 3:00 pm (0600 GMT) the local fire department received a call saying it appeared that a plane had crashed into the lake, the reports said.

The reports added, citing defence ministry sources, that the training plane had disappeared from the radar.

The defence ministry was not able to immediately confirm details to AFP.

Jiji Press said the local municipality had said there had been no damage to houses in the area.