Transcript for Investigation of military accident off the coast of Japan

And there is a breaking headline tonight. A military accident involving a marine fa-18 and a kc-130, plunging into the sea off the coast of Japan. Several American servicemembers onboard, and there is a search and rescue mission under way at this hour. Here's ABC's chief global affairs correspondent Martha Raddatz tonight. Reporter: The midair mishap was in the middle of the night, in cloudy skies 200 miles off the coast of Japan. Both aircraft ended up in the water, indicating a midair collision. Details are still unclear, but the f-18, like this one, may have been attempting to refuel off of the kc-130. Two were aboard the fighter jet, which does have ejection seats, and five aboard the refueler. It was the Japanese defense forces that found the one marine alive, but the search continues. And Martha Raddatz back with us tonight, of course, Martha, the focus is on the search that's under way at this hour, but you've learned that the investigation into the cause is already under way tonight? Reporter: Absolutely, David. They'll look at whether weather was a factor, whether fatigue was a factor. But this is really a grim reminder of how even these training missions for the military can be so dangerous. All right, Martha Raddatz, we're thinking of all those families tonight. Thank you.

This transcript has been automatically generated and may not be 100% accurate.