OCRACOKE, N.C. -- A fourth worker who had been preparing for an Independence Day celebration died from injuries suffered when a truckload of fireworks exploded on a dock at a remote North Carolina island, authorities said.

The workers were unloading fireworks from the truck when it blew up, catching the attention of residents and tourists across the village.

Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives were at the scene Sunday investigating what caused the blast, Tunnell said.

Dock master Robert Raborn noticed the workers unloading the truck Saturday from the Anchorage Marina about 200 yards away and described the explosion as one of the loudest things he has ever heard.

"It was like 40 minutes worth of fireworks going off in four seconds," Raborn said.

Authorities have not released the names of the workers, four men and one woman.

The crew worked for Melrose South Pyrotechnics near Rock Hill, S.C. The company said in a statement it had sent an official to work with investigators.

The explosion stopped ferries to the island for a few hours, but service was restored later Saturday. The island is accessible only by boat or air, and it is hours away from any major city. There is a small health center and volunteer fire department on Ocracoke, but not much else.