A Kilo-class Russian submarine appears to be on fire in a video which appeared online. However, the country's government has said that the incident was part of a planned "exercise", which seems debatable going by the footage.

The video, shared by several users on Twitter, shows thick black smoke and a raging fire near five submarines docked in Russia's Pacific port city of Vladivostok, with the rear of a vessel seemingly on fire.

The situation appears quite grim for the submarines, which look similar to Russia's Kilo-class diesel-electric attack vessels, according to Popular Mechanics.

However, because the clip is unclear due to all the smoke, it cannot be said for certain if the submarine is actually on fire. The authenticity of the video has also not been verified.

Russia's Pacific Fleet released a press statement saying that the fire was a part of their planned "damage control exercise". Apart from this, not many details regarding this particular exercise and the specifics of the submarines involved were revealed.

Another video, posted on YouTube, shows the fire from a different point of view.

Kilo-class submarines are non-nuclear vessels which have been crucial for Russia since the 1980s.

It is worth noting that the Russian navy is not the only one operating these submarines. India had the INS Sindhurakshak, a similar submarine that suffered a tragic fate after a fire in the weapon's bay triggered a massive explosion, destroying the vessel and killing 18 onboard.

Russia's kilo-class submarine
A file photo of a Russian Kilo-class submarine REUTERS/Murad Sezer