Thousands of people are protesting in the Siberian city of Kemerovo, angry at Russian officials over the leisure complex fire that killed at least 64 people, 41 of them children.
President Vladimir Putin arrived in Kemerovo earlier and blamed “criminal negligence” for Sunday’s blaze.
Relatives say as many as 85 people are still missing, most of them children, according to Interfax news agency.
Investigators say the fire alarm was switched off and exits were blocked.
Some 300 people rallied outside the local government headquarters on Tuesday, demanding that officials be sacked over the fire safety shortcomings.
The cause of the fire is not yet known, but Russia’s Investigative Committee has spoken of “serious violations” at the Winter Cherry mall.
Wednesday will be a day of mourning throughout Russia, Mr Putin has decreed.
A woman in the Kemerovo crowd drew applause when she said “children called their parents, asked them for help, asked for the fire brigades to be sent in”.
Officials were booed when they urged the crowd to disperse, after the protest had already lasted seven hours, Russia’s RIA news agency reported.
Regional deputy governor Sergei Tsivilev then got down on his knees to beg forgiveness, and was applauded by the crowd.
‘There was no panic – she was saying goodbye’
At the scene: Sergei Goryashko and Elizaveta Fokht, BBC Russian
Kemerovo residents’ anger has built up since Sunday and it burst forth at the rally of several thousand outside the city administration building.
The main slogans were “Truth!” and “Resign!” – directed at local officials.
The most active among them was Igor Vostrikov, whose wife, sister and three children – aged two, five and seven – all died in the fire.
Deputy governor Sergei Tsivilev accused him of trying to gain publicity out of the tragedy. Igor’s reply was that his entire family had suffocated in the cinema, unable to escape because the doors were locked.
Fighting back tears, he described his wife’s last moments, when she phoned him, short of breath. “There was no panic – she was saying goodbye.”
“I have nothing more to lose,” he said.
Dozens of people vowed to stay on the square until governor Aman Tuleyev resigns.
President Putin also expressed indignation over the disaster – though he did not speak to the crowd.
“What is happening here?” he said, after laying a wreath. “This is no battle or an unexpected methane outburst in a mine.”
“People, children came to relax. We are talking about demography and are losing so many people because of what? Because of criminal negligence, sloppiness.”
The mall’s shops, cinema and bowling alley were packed at the time as it was the beginning of the school holiday.
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.
Kemerovo mall fire: How party turned into nightmare
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?”
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.