Firefighters work to extinguish fire at the Roslyakovo shipyard in the northern Russian region of Murmansk, in this still image taken from video, December 29, 2011. [Photo/Agencies]

MOSCOW - Nine firemen were hospitalized Friday after being poisoned by smoke when trying to extinguish a fire on a nuclear submarine in northern Russia, Interfax news agency reported.

The Yekaterinburg nuclear submarine caught fire at a shipyard in Russia's northern city of Murmansk on Thursday.

Emergency Situations Ministry had said no deaths or injuries were reported, but media reports later said some crew still remained aboard the vessel. The fire has been contained at early hour on Friday and was expected to be eventually put out "in the coming hours," Emergency Situations Minister Sergei Shoigu said.

Radiation levels in the area remain normal, said a local source, adding that the submarine's reactor had been shut down before its routine maintenance started.

A criminal investigation has been launched into the fire.

Yekaterinburg is one of Russia's seven Delta-IV class submarines in service, which are all deployed in the Northern Fleet. It is capable of carrying 16 Sineva submarine-launched ballistic missiles.