KITTERY, Maine â€"  A fire on a nuclear-powered submarine at a Maine shipyard has injured six people, including a firefighter.

Fire crews responded Wednesday to the USS Miami SSN 755 at the Portsmouth Naval Shipyard on an island in Kittery, a town near Portsmouth, N.H., popular with tourists.

The shipyard says the injured people have been treated and released. The firefighter suffered heat exhaustion.

The fire still was not out shortly before midnight but shipyard spokesman Capt. Bryant Fuller says the situation is improving.

Shipyard public affairs specialist Gary Hildreth says the fire started in the forward compartment of the sub. The shipyard says the sub's reactor wasn't operating at the time and was unaffected.

The cause of the fire hasn't been identified.