Aerial footage broadcast on Japanese TV showed the wreckage of the crashed helicopter surrounded by trees in Gunma prefecture, northwest of Tokyo, and officers in navy uniforms examining the site.
"Eight people were found near the site, but we don't know their condition," a defence ministry official told AFP.
But the helicopter did not return by its scheduled arrival time and lost contact with air traffic control, said Hiroshi Yoshida, a local official.
Passengers included disaster management officials and firefighters, he added.
Helicopter accidents are not rare in Japan.
In February, two pilots were killed in a military helicopter crash in southern Japan.
It went down seven minutes after takeoff, slamming into and setting on fire a house that was completely destroyed in the accident.
And last year, nine people aboard a helicopter were killed after it crashed during a mountain rescue drill.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)