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.
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 time.
Russian officials and state media have been playing down the latest accident.
“Of course when a 70-tonne crane falls on deck, it will cause harm,” conceded Alexei Rakhmanov, head of the United Shipbuilding Corporation which runs the shipyard.
“But according to our initial information, the damage from the falling crane and from the ship listing when the dock sank is not substantial.”
‘Modernisation to continue’
The Admiral Kuznetsov, which was commissioned in 1985, is undergoing a multi-million dollar overhaul and was due to return to service in 2021.
A spokesman for the factory operating the floating dock said that experts had checked the ship and found “no damage yet that could affect its functioning”.
“The crane fell on to the deck near the technical zone, the loading area,” Evgeny Gladyshev told the BBC. He said the area affected had been slated for repairs, and had already been partly dismantled in any case.
The aircraft carrier has now been transferred to another shipyard, Ria news agency reports. Officials say its “modernisation” will continue – as well as the extra repairs.
“Work has already started. We will try to keep to the deadline,” Mr Gladyshev said.
In a video statement released via social media, the governor of Murmansk said a team of rescue divers from the navy’s Northern Fleet was still searching for the missing worker.
Two of the injured have been admitted to hospital.
It is unclear whether the 330m-long dry dock itself can be salvaged.
“Even if this is technically possible, the operation will not be easy and, most probably, very expensive,” a spokesman for the shipyard said.
Russian aircraft carrier Admiral Kuznetsov damaged by crane