A group of gunman have opened fire at audience members in a concert hall near Moscow just weeks after the UK and US warned Russia faces an impending terrorist attack.

Russia's human rights commissioner Tatyana Moskalkova labelled the incident, which reportedly took at least 12 lives, a "terrorist attack".

The British Embassy in Moscow echoed concerns about the attack, saying: "We are aware of reports of a terrorist incident around the Crocus concert hall in Krasnogorsk near Moscow. British nationals should avoid the area and follow instructions of local authorities."

Popular pro-Kremlin channel Readovka claimed around 50 people sustained injuries at Crocus City Hall.

The venue also witnessed two explosions, Russian news agencies have claimed.

Three camouflage-clad gunmen reportedly entered the venue and soon opened fire.

Telegram channel Baza shared a video showing flames and a huge plume of smoke rising from what was said to be the concert venue.

As many as 100 people were also rescued from the basement of the concert hall, emergency officials at the venue have claimed.

Russian news agencies later revealed people were still stuck on the roof of the building.