At least five camouflage-clad gunmen with automatic weapons burst into the packed concert hall in the city’s western suburbs on Friday night as the audience was gathering to watch the veteran rock band Picnic, shooting into the crowd and setting off explosives that started a massive fire, according to Aljazeera.

Russian investigators said more than 60 people had been killed. Health officials said about 145 people were injured, and about 60 of them were in critical condition.

ISIL, the hardline group that once sought control over Iraq and Syria, claimed responsibility for the attack on its Telegram channel, saying the gunmen had escaped. It was not possible to independently verify the claim.

The concert hall, one of the most popular in Moscow, can hold some 6,200 people.

Alexei, a music producer, was about to settle into his seat ahead when he said he heard “several machineguns bursts” and “a lot of screams”.

“I realised right away that it was automatic gunfire and understood that most likely it’s the worst: a terrorist attack,” Alexei told the AFP news agency, declining to share his full name.

As people ran towards the emergency exits, “there was a terrible crush” with concertgoers climbing on one another’s heads to get out, he added.

The attack, which left the concert hall in flames and its roof in a state of collapse, was one of the worst in Russia since the 2004 Beslan school siege in which more than 330 people, half of them children, were killed. The death toll appeared set to rise, according to unconfirmed reports.

Moscow Mayor Sergei Sobyanin said Friday’s raid was a “huge tragedy.” President Vladimir Putin was being given continuous updates about the situation, according to his spokesman Dmitry Peskov.