Factbox-What we know about the shooting at a concert venue near Moscow

Russian news agencies reported multiple casualties after a shooting incident at a concert venue near Moscow on Friday.

Here's what is known about the shooting so far:

-Unidentified gunmen opened fire at the Crocus City Hall in Krasnogorsk near Moscow on Friday evening during a concert of the band "Picnic".

-Forty people are reported dead and more than 100 wounded after the shooting as of 1915GMT, Russian state news agencies said, citing Russia's Federal Security Service (FSB).

-The Interfax news agency reported up to five gunmen were involved in the attack.

-Russian prosecutors called the attack "an act of terrorism" and have opened a criminal case.

-An eyewitness told Reuters reporters outside the venue that automatic weapons had been used.

-Video posted online by Russian news agencies showed billowing clouds of smoke and flames rising from the venue building.

-TASS reported that people remained inside the building, which is almost completely engulfed in flames and that others were trapped on the roof.

-Special units of Russia's national guard as well as police and firefighters are on the scene, TASS said.

-Moscow's mayor cancelled all large-scale public events over the weekend.