Russia tried to submerge a burning nuclear submarine at a navy shipyard on Thursday after battling for hours with helicopters and tug boats to bring the raging blaze under control.

There was no radiation leak, authorities said.

Television pictures showed a giant plume of smoke above the yard in the Murmansk region of northern Russia as over 100 firemen struggled to douse flames which witnesses said rose 10 meters (30 feet) above the stricken vessel.

Emergency workers said efforts to partially sink the submarine at the dock had failed to fully extinguish the fire. A defense ministry spokesman quoted by state news agency RIA said the blaze, which began at 1220 GMT (7:20 a.m.), was under control more than eight hours later.

Russia said the nuclear reactor had been shut down and all weapons had been removed from the 167-metre (550 feet) Yekaterinburg, which launched an intercontinental ballistic missile from the Barents Sea at a firing range thousands of miles away in Kamchatka as recently as July.

Radiation levels are normal, a spokeswoman for the emergencies ministry said. No one was injured.

After hours of trying to put out the flames, officials decided to partially submerge the hull of the 18,200-tonne submarine at the Roslyakovo dock, one of the main dockyards of Russia's northern fleet 1,500 km (900 miles) north of Moscow.

Local media reports were vague, but the blaze was believed to have started when wooden scaffolding caught fire during welding repairs to the submarine, which had been hoisted into a dry dock.

The submarine can carry 16 ballistic missiles, each with four warheads. Its nuclear reactor was not damaged in the fire and Russian navy submarine reactors are built to withstand enormous shocks and high temperatures.

The reactor has been shut down and does not pose any danger, Interfax news agency quoted a source at navy headquarters as saying.

Russia's worst post-Soviet submarine disaster occurred in August 2000 when the Kursk nuclear submarine sank in the Barents Sea killing all 118 crewmen aboard.