OCRACOKE, N.C. — A worker preparing for an Independence Day celebration was killed and four colleagues critically injured after fireworks exploded Saturday morning on a remote North Carolina island dock, authorities said.

The explosion shook homes and businesses and was heard across a village on the southern end of Ocracoke Island, which is the only inhabited part of the 15-mile spit of land.

The island is only accessible by boat or plane, and three medical helicopters took the injured workers to hospitals, Hyde County spokeswoman Jamie Tunnell said. Two came from a hospital in Greenville, N.C. — about an 85-mile flight. The other came from a burn center in Chapel Hill, about 180 miles away.

Several doctors, including a medical examiner, and a nurse who were visiting the island helped paramedics and staff from the local health clinic treat the workers, Tunnell said.

She did not release the names of the workers, the company involved with the fireworks or any information on what might have caused the blast.

Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives and other federal officials are coming to the island to investigate.

Dock master Robert Raborn noticed the workers unloading the truck from the Anchorage Marina about 200 yards away. He heard the explosion, which he described as one of the loudest things he has ever heard, then turned to see what happened.

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

Hundreds of tourists and residents streamed down to the south end of the island to see what was going on, Raborn said.

The explosion stopped ferries to the island for a few hours, but service was restored around noon Saturday.

By the afternoon, things were returning back to normal. But Bob Chestnut, owner of the Ride the Wind surf shop, said the explosion reminded residents of how isolated they are — hours away from any major city. There is a small health center and volunteer fire department, but little else.

“How do you get help here? How do you get enough people out to fight something?” Chestnut said. “That’s the thing we’re thinking about.”