Russia's only aircraft carrier, the Admiral Kuznetsov, was damaged when the dry dock where it was undergoing a refit sank, sending a giant crane crashing on to the ship.
Rescuers are searching for a missing ship-worker.
Four others needed medical attention after falling into the icy sea.
Russian officials insist the damage is “not critical” but the 70-tonne crane caused a gash on the Kuznetsov's deck of up to 5m (16ft).
The Admiral Kuznetsov was being overhauled at one of the world's largest floating docks near the northern city of Murmansk.
Recent accidents
The carrier played a prominent role in Russia's military campaign in Syria, where Russian fighter jets are supporting troops loyal to President Bashar al-Assad.
It was at the centre of two accidents during its mission in the Mediterranean in late 2016. A MiG fighter jet crashed into the sea as it approached the ship and an Su-33 crashed on landing when a cable broke, and the plane rolled off the deck.
In January 2017, it was dubbed the “ship of shame” by the UK's then Defence Secretary, Michael Fallon, as it returned from its mission, sailing close to the UK coast. The ageing carrier sparked mocking headlines as it passed, belching clouds of black smoke.
The PD-50 dock sank after a power cut led to rapid flooding of its ballast tanks. Both its cranes collapsed, one hitting the aircraft carrier which was exiting the dock at the…
