11 troops missing after helicopter crash off Florida

Update: A Pentagon official said all 11 service members were presumed dead.

PENSACOLA, Fla. -- Seven Marines and four soldiers were missing early Wednesday after an Army Blackhawk helicopter crashed during a night training exercise out of Eglin Air Force Base in the Florida Panhandle.

Base officials said the Marines are part of a Camp Lejeune, North Carolina-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 spokesperson Andy Bourland said.

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

The National Weather Service had issued a Dense Fog Advisory for the region where the helicopter went down, but there was no early indication whether the fog had any role in the crash. It was still foggy at dawn Wednesday, base officials said.

CBS News correspondent David Martin reports the aircraft went down over water.

The fog was the reason it took several hours for search and rescue teams to locate debris, which had washed ashore, Martin says.

The hunt for survivors was being hampered by the fog and searchers faced the prospect of waiting for the sun to burn off some of the fog, Martin adds.

Names of those involved were being withheld pending notification of next of kin, Bourland said.

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

He said a second Blackhawk helicopter taking part had returned safely to the base and all on board were accounted for.

The UH-60 helicopter went down off a remote swath of beach between Pensacola and Destin, base officials said. 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.