The area where the crash happened Tuesday night was under a fog advisory. The area was still extremely foggy Wednesday morning, which was affecting the search, Eglin public affairs specialist Sara Vidoni said.

Base officials said the Marines are part of a Camp Lejeune-based special operations group and the soldiers were from a Hammond, Louisiana-based National Guard unit. The helicopter was reported missing around 8:30 p.m. Tuesday and search and rescue crews found debris from the crash around 2 a.m. Wednesday, Eglin spokesman Andy Bourland said.

"At this time all are missing," Bourland said.

Names of those involved were not immediately released, pending notification of next of kin, he said.

Bourland said the Army helicopter took off from a nearby airport in Destin and joined other aircraft in the training exercise.

The UH-60 Black Hawk helicopter went down during a routine training mission on a remote swath of beach between Pensacola and Destin. The beach is owned by the military and is used for test missions.

The training area includes 20 miles of pristine beachfront that has been under the control of the military since before World War II. Military police keep a close watch on the area and have been known to run off private vendors who rent jet skis or paddle boards without permission.

Test range manager Glenn Barndollar told The Associated Press in August that the beach provides an ideal training area for special operations units from all branches of the military to practice over the water, on the beach and in the bay.

The military sometimes drops trainees over the water using boats or helicopters and the trainees must make their way onshore.