VLADIVOSTOK, Russia — A fire burned for five hours on an atomic-powered submarine undergoing repairs near Russia's eastern port of Vladivostok on Monday, but naval and shipyard officials said there was no risk of a radiation leak and nobody was hurt.

Black smoke poured from the submarine Tomsk, which is powered by two nuclear reactors, after it caught fire at the Zvezda shipyard in Bolshoi Kamen, about 25 kilometers (15 miles) across a bay from Vladivostok on the Sea of Japan, authorities said.

The fire was the second on board a Russian nuclear-powered submarine in lass than two years.

"There is no threat of radioactive contamination," the state-run Itar-Tass news agency cited an unidentified official in Russia's Pacific Fleet command as saying. Regional emergency officials said radiation levels in the area were within the normal range.

After the fire was extinguished, firefighters continued to douse the area to ensure it did not flare up again, the state-owned United Shipbuilding Corporation, which operates the shipyard, said in a statement.

It said there were no casualties and both reactors had been shut off and were in "safe condition". The firm also said there had been no weapons aboard the ship, which normally carries up to 24 guided missiles, when the fire broke out.

When a blaze engulfed the atomic-powered Yekaterinburg at a shipyard in northwestern Russia in December 2011, official statements said there had been no nuclear missiles on board the sub, but a respected magazine later cited several unnamed sources as saying this was untrue.

Navy sources said on Monday that, in addition to two firefighting vessels, a ship that monitors radiation levels had been sent to the area, Russian news agencies reported.

The fire started in a ballast area of the submarine during welding works after an acetylene torch was used to cut through a grate, setting a rubber seal, cables, and paint on fire, RIA cited an unnamed official at the shipyard as saying.

The official said the cistern was outside the sealed core of the submarine where the reactors are located, according to RIA.

Russia's navy has suffered several fatal accidents since the collapse of the Soviet Union in 1991.

The nuclear-powered submarine Kursk sank in the Barents Sea in 2000, killing all 118 crewmen aboard, and 20 people died aboard the submarine Nerpa in 2008 when its fire extinguishing system went off, flooding compartments with deadly gas.