This file photo shows an aircraft carrier undergoing repairs at the Roslyokovo facility in 2006 [Reuters]

One of Russia's largest nuclear submarines caught fire while undergoing repairs at a dock in the northern port of Murmansk but no radiation leaks have occurred, officials say.

The 11,740-tonne Yekaterinburg was not carrying any nuclear missiles or conventional rockets while at the Roslyakovo dock, near Russia's border with Norway, a defence ministry spokesman said.

The fire began during repair work, and quickly spread from the shipyard's wooden structures to the submarine's outer hull, Vadim Serga, a spokesman for the Russian Navy's Northern Fleet, told the Interfax news agency.

A massive operation was launched by emergency workers to control the blaze, employing 11 fire brigades and a navy fire boat. Television footage showed huge clouds of smoke billowing from the shipyard even after the flames had been contained.

"I would say the flames reached about 10 metres," one unnamed witness told the TV-21 television station.

A defence ministry spokesman told Russian state television that the submarine's two reactors had been switched off well in advance and there was "no threat of a nuclear radiation leak".

"The power unit was switched off and is now safe," Igor Konashenkov, defence ministry spokesman, said.

The Delta-IV class vessel was commissioned by the former Soviet Union in 1985 and can carry up to 16 inter-continental ballistic missiles, according to Russian press descriptions of the submarine.

Russia is believed to have six Delta IV class submarines, which form the backbone of its sea-based nuclear defences.

The last major accident to hit the Northern Fleet occurred in August 2000, when the Kursk nuclear submarine caught fire and exploded while at sea.

Military prosecutors have launched a check into the causes of the fire.

Jet crash

In a separate military incident on Thursday, a Sukhoi-24 fighter jet crashed on landing in the southern region of Volgograd.

Both pilots were able to eject and were unharmed, the Russian defence ministry said.

"The plane exploded during landing," said a ministry spokesman quoted by Interfax. "The crew ejected following orders."

That accident occurred after a routine training flight at the Marinovka aerodrome 60km from the city of Volograd.

Source: Agencies