The Defence Ministry in Russia says the atomic reactor of a nuclear submarine that caught fire on Thursday has been shut down.
The Emergency Ministry says no one was injured in the fire and radiation levels are normal at the shipyard in Murmansk where the fire occurred.
Television pictures showed thick smoke billowing from the top of the Yekaterinburg as firefighters in helicopters and tugboats battled the blaze.
Russian media say wooden structures in the dock caught fire and the blaze spread to the vessel.
Interfax news agency reported that all weapons had been removed before the repair work started.
The Yekaterinburg is a Delta-IV-class nuclear submarine.
It was commissioned by the Soviet Union in 1985 and can carry 16 intercontinental ballistic missiles, the BBC reports.
A Russian nuclear submarine, the Kursk, sank in the Barents Sea in August 2000 killing all 118 crewmen aboard.