Search on for 11 missing US military personnel after Black Hawk crash

Eleven US military personnel are missing after an Army Black Hawk helicopter crashed during a night training exercise in Florida.

A spokesman for Eglin Air Force Base in the state's north confirmed a search is underway for survivors, CNN reports, although a Pentagon official was quoted as saying all those onboard are presumed dead.

"Debris from the aircraft was located by a search and rescue team at about 2am this morning," the statement read.

"Search and rescue efforts are underway at the accident site currently."

Four air crew and seven marines from North Carolina were reportedly onboard the UH-60 Black Hawk.

A second Black Hawk on the training mission returned to Eglin.

The training exercise reportedly took place in heavy fog.