The F-18, a twin-engine supersonic aicraft used by the US Navy, came down in waters near Naval Air Station Key West in Florida on the US east coast. 

Two pilots ejected from the aicraft at around 4.30pm local time, according to the US Navy.

Tragically it has since been confirmed the two inside the aircraft died.

The plane, part of Virginia-based Strike Fighter Squadron 213, burst into flames before crashing into the water, witnesses say. 

Pictures posted to social media show a military helicopter hovering over the apparent crash site.

Barbie Wilson, who lives nearby and witnessed the crash, said she "saw fire" and "then [the jet] just dropped".

The jet crashed during a training mission near Naval Air Station Key West, a military facility that houses air-to-air combat fighter aircraft.

A blaze engulfed the jet before it crashed around a mile away from the runway, a witness told Local 10 News. 

Both pilots managed to parachute out of the jet, a Naval Air Station Key West spokesman told the station. 

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