Several United States (US) Marines are missing following a still-unexplained accident off the coast of Japan.

US Officials say two Marine Corps jets might have collided mid-air on Thursday during a refueling exercise that went fatally wrong.

Seven soldiers were involved but so far two have been found.

One was been pulled to safety from an F-18 fighter jet and another was found 10 hours after the collision and brought aboard a Japanese military vessel.

Japan’s Defence Minister says that person is in a stable condition and Japanese forces will do their utmost to rescue the six missing.

In a statement the Marine Corps said the F-18 and a refueling jet were involved in what they called a mishap and that the two were conducting regular training.

They didn’t elaborate on the nature of the incident.

US military aviation accidents around the world have jumped nearly 40% in four years, killing at least 133 service members, according to the Military Times.

It’s prompted hearings in Congress to address the rise.