Fire broke out late Wednesday aboard a nuclear-powered U.S. Navy submarine docked at a shipyard in Maine.

Officials at the Portsmouth Naval Shipyard in the town of Kittery say the fire started in the USS Miami's forward compartment. The submarine's nuclear reactor was not operating at the time of the fire, and was unaffected.

At least six people were injured in the fire. All nonessential personnel aboard the USS Miami were ordered to evacuate when the fire broke out.

The cause of the fire has not been determined.

The USS Miami has been docked at Portsmouth for system upgrades and maintenance since March. The submarine's home port is a U.S. Navy base in Groton, Connecticut.