Hyde County spokeswoman Jamie Tunnell told CBS Affiliate WRAL that everyone hurt Saturday worked for a company setting up the fireworks show on the town's docks.
Anchorage Marina dock master Robert Raborn said the explosion was heard across Ocracoke village.
Raborn says from his vantage point 200 yards away, it looked like 40 minutes worth of fireworks went off in four seconds.
Tunnell said three medical helicopters from Greenville and Dare County transported victims. A helicopter was also dispatched from Norfolk, Va., but wasn't needed, a Sentara General Hospital spokesman said.
At least one victim was flown to the North Carolina Jaycees Burn Center at UNC Hospitals in Chapel Hill.
Authorities say no danger remains, and ferries are running again.
An employee for Melrose Pyrotechnics told WRAL that the Catawba, S.C.,-based company had a crew there to handle the town's fireworks.
Restaurant owner Scott McNally, who was about 100 yards from the blast, said employees were unloading fireworks from the parked truck when the explosion occurred. He told WRAL it sounded like a plane crashing into a building.
Ocracoke Island is on the southernmost tip of North Carolina's Outer Banks and is accessible only by ferry and private plane or boat.
Ferry service to the island was suspended temporarily but has resumed.
CBS Affiliate WNCT reports that the FBI, the Explosive Ordinance Disposal Company and the Bureau of Alcohol, Tobacco, Firearms and Explosives are evaluating the scene.