Four workers have been injured and one remains missing after Russia's only aircraft carrier, the Admiral Kuznetsov, suffered damage when a floating dry dock sank while the vessel was leaving it, officials say.

The waterborne repair station's sinking at an Arctic shipyard early on October 30 was the latest in a series of mishaps involving the Admiral Kuznetsov, which lost two military jets in accidents off the coast of war-torn Syria in 2016.

The PD-50 dry dock had "fully sank" by 3:30 a.m. local time at the 82nd Repair Shipyard in the village of Roslyakovo near the port city of Murmansk, regional Governor Marina Kovtun said on Twitter.

She said that two injured workers were hospitalized and two were treated without hospitalization.

"Unfortunately, one person has not yet been found," Kovtun said, adding that rescue divers were working at the site.

Hours later, authorities said that the divers were suspending their operations for the night due to darkness and that the missing worker had not been found.

• Amos Chapple

On October 21, Russia's only aircraft carrier steamed through the English Channel on its way to Syria. Given the seemingly limited effectiveness of the 305-meter Admiral Kuznetsov, many analysts believe the attention that the vessel is generating is the real aim of its rare, and very public, outing.

Originally published October 2016

One of the injured was in very serious condition, said Viktor Rogalyov, the head of the local Disaster Medicine Center.

Kovtun said that rescue divers from the Russian Navy's Northern Fleet were working at the site and that it was "hard to say" what caused the sinking.

Authorities said at least one crane fell when the dry dock sank, damaging the aircraft carrier, but that the damage was above the waterline and was not severe.

Aleksei Rakhmanov, head of the state-run United Shipbuilding Corporation, said experts are assessing the damage but that "the vitally important parts of the aircraft carrier were not affected."

The PD-50 was one of the world's largest dry docks.

Russia sent the 305-meter Admiral Kuznetsov to the Eastern Mediterranean in 2016 as part of its ongoing military campaign in support of Syrian government forces in the Middle Eastern country's devastating war.

An Su-33 military jet crashed while trying to land on the aircraft carrier there in December 2016, and a MiG-29 crashed a few kilometers from the vessel three weeks earlier.

A fire on board the carrier killed a sailor during a 2008-09 deployment, and an oil spill was spotted by the Irish Coast Guard near the vessel afterwards.

With reporting by TASS, RIA Novosti, and Interfax