Matthew Prior, 48, killed, after a diving accident near Duck Key in Monroe County.

A local man died Wednesday afternoon while diving offshore in Florida during a trip with his family, according to the Monroe County, Fla., Sheriff's Office.

Sheriffs said Matthew Prior, 48, was with a group of individuals diving on a hooka rig off Duck Key on a vessel named "Seafari."

Witnesses told sheriffs Prior had been underwater for "about 15 minutes" when he indicated he wanted to surface.

Prior indicated "several times he was alright" to an instructor before signaling he wanted to surface, although he "suddenly became unresponsive" while surfacing, according to sheriffs.

Sheriffs said the instructor grabbed Prior, brought him to the surface and called for help. Prior was taken aboard the boat, where CPR was performed.

All divers and snorkelers were gathered and the boat headed back to shore.

Prior was pronounced dead at Fishermen's Hospital. An autopsy will be done to determine the cause of his death.