Search and rescue operations were underway following a "mishap".
The C-130 was thought to be carrying 5 servicemen and the F-18 two, said the Japanese official, who added that Japan had scrambled 4 aircraft and 3 ships in the search.
"The aircraft involved in the mishap had launched from Marine Corps Air Station Iwakuni and were conducting regularly scheduled training when the mishap occurred", according to a Marine Corps Base Camp Butler statement on Wednesday.
The Marine Corps said Japanese search-and-rescue aircraft immediately responded to aid in recovery efforts. Very few details have been made public in the initial Corps news release. "The aviators retained their wings and will continue service to their country as valued members of 3rd Marine Aircraft Wing", he said.
The statement concluded by saying that "the investigation is ongoing" and "no other information is yet available".
Early reports that surfaced on Twitter report that an F/A-18 (unspecified variant) and a C-130 crashed into the sea with a total of seven crewmembers on board.
This is a developing story; check back for more updates.