The fire which killed 64 people, many of them children, at a leisure complex was caused by “criminal negligence”, President Vladimir Putin has said.
Visiting the scene in Kemerovo, Siberia, Mr Putin berated “sloppiness”.
Investigators say the fire alarm was switched off and exits were blocked when the fire started on Sunday.
Interfax news agency reported that some 300 people gathered outside the local government headquarters demanding the dismissal of authorities.
The cause of the fire is not yet known, but Russia’s Investigative Committee has spoken of “serious violations” at the Winter Cherry mall.
This is “no battle action or an unexpected methane outburst in a mine,” Mr Putin said after laying a wreath at the scene.
“People, children came to relax. We are talking about demography and are losing so many people because of what?
“Because of criminal negligence, sloppiness.”
Sunday’s blaze started on an upper floor. The mall’s shops, cinema and bowling alley were packed at the time.
Video on social media showed people jumping from windows to escape.
The Investigative Committee says a fire safety technician at the complex “switched off the alarm system” after being alerted about the fire.
It said a criminal investigation had begun.
Five people have been arrested including the official suspected of deactivating the public address system.
In a Facebook post (in Russian), Kemerovo politician Anton Gorelkin said that “fire exits were shut, turning the complex into a trap” and “there was no organised evacuation”.
He also said a fire extinguisher that could have doused the flames at the start did not work.
The region’s deputy governor, Vladimir Chernov, said “this is the question: Why were the doors shut?”
The fire broke out at about 17:00 (10:00 GMT) on Sunday.
Mr Chernov was quoted as saying the fire probably began in the children’s trampoline room.
“The preliminary suspicion is that a child had a cigarette lighter which ignited foam rubber in this trampoline room, and it erupted like gunpowder,” he said.
However, Rossiya 24 TV, a national broadcaster, said an electrical fault was the most likely cause – as in most previous deadly fires in Russia.
Russia’s deadliest fires
2009 – 156 people die in a Perm nightclub inferno in the Urals region, Russia’s worst fire in recent years (fireworks and lack of exits blamed)
2007 – Fire engulfs a rural old people’s home in the southern region of Krasnodar, killing 63 (burning cigarette blamed)
2006 – 46 die in Moscow narcological hospital fire (arson blamed)
2003 – A hostel fire at the Russian People’s Friendship University in Moscow kills 44 (lack of safety measures blamed)
1999 – Fire engulfs the police headquarters in the southern city of Samara, killing 57 people (burning cigarette blamed officially, but arson by criminals not ruled out)
Source: Interfax news agency
There are unconfirmed reports that some mall guards prevented children from fleeing down staircases.
Kemerovo region has declared three days of mourning, and locals are leaving flowers and cuddly toys at a makeshift memorial near the complex.
An Instagram post from Kemerovo showed a big queue of volunteers waiting to donate blood at a clinic.
Who were the victims?
At least nine of the bodies found so far are children.
As well as those killed, 11 injured victims are being treated in hospital, suffering from smoke inhalation.
The most serious case is an 11-year-old boy whose parents and siblings died in the fire, Health Minister Veronika Skvortsova said. He reportedly fell from the fourth floor and is in intensive care with multiple injuries.
Officials says 56 bodies have been recovered and the remains of 21 have been released to relatives for burial.
Kemerovo lies about 3,600km (2,200 miles) east of Moscow.
The shopping centre, covering 23,000 sq m (248,000 sq ft), opened in 2013. It includes a petting zoo, all of whose animals are reported to have died.
Yevgeny Dedyukhin, deputy head of the Kemerovo region emergency department, said the area of the fire was about 1,500 sq m.
“The shopping centre is a very complex construction,” he said. “There are a lot of combustible materials.”