Firefighters in France extinguished a blaze on board a nuclear-powered submarine on Saturday after a 14-hour battle, the defence ministry said.
The fire broke out on the vessel, named La Perle (The Pearl), while it was in dry dock for renovations.
France’s defence ministry said no one was injured, and insisted that the risk of radioactive contamination was “zero” because the submarine’s nuclear fuel and arsenal of weapons had been removed ahead of the maintenance work.
Local newspaper Var-Matin published images of white smoke rising from the port, and reported that some of those aboard fled via the submarine's torpedo holds.
At least 100 firefighters from three services, backed up by specialist naval teams including a support ship, took more than 14 hours to put out the fire at the southern naval base in Toulon.
The blaze broke out in a hard to reach part of the lower bow at around 10.30am on Friday morning, the French navy said.
The extent of the damage to the vessel was not immediately clear, but an official with the Naval Group repair centre on Friday called the incident "serious".
Defence Minister Florence Parly is due to visit the site.
The vessel, which can take its crew of 70 down to depths of up to 300 metres, is an attack submarine used for tracking ships, escorting aircraft carriers, carrying out coastal reconnaissance operations, and deploying special forces.
In addition to its six nuclear-powered attack submarines, France also operates four nuclear ballistic missile submarines.
Toulon is France's biggest naval base and is home to most of its fleet, including the nuclear-powered aircraft carrier Charles de Gaulle and the nuclear submarines and other warships that escort it on its missions.
The submarine, which entered service in 1993, docked at Toulon in January for 18 months of renovation work that was to keep her operational until the end of the decade.