Seven Marines and four crewmembers are missing and presumed dead Wednesday after an Army helicopter crashed during a training exercise off the Florida Panhandle.

The area was under a fog advisory when the crash occurred Tuesday night near Eglin Air Force Base about 50 miles east of Pensacola. The extreme fog still present Wednesday morning impeded the search, grounding a Coast Guard helicopter until about 1 p.m. CT.

“We’re still in search and rescue mode,” Maj. Gen. Glenn Curtis, adjutant general of the Louisiana National Guard, said in a news conference in Hammond, La., the New Orleans suburb where the National Guard unit has its headquarters.

The search will continue through the night, Elgin spokesman Mike Spaits said.