Seven of the eight injured people were treated at hospitals and were released. One sailor remained hospitalized after undergoing surgery for a broken arm.

U.S. Navy officials said they were still trying to determine what caused the blast, which occurred around 9 a.m. at the Earle Naval Weapons Station in Middletown. Navy spokeswoman Beth Baker said it occurred while personnel were doing routine maintenance on a 27-foot aluminum utility boat, which is used to support port operations at the base.

The blast was confined to a boathouse where the maintenance was being done.

The names of the sailors and the Department of Defense firefighter injured in the blast weren't immediately disclosed, and further details on their injuries weren't provided.

The station provides ammunition and explosives for Navy vessels. Baker said ammunition and ordnance operations there were unaffected by the explosion, which was deemed an accident.