Hundreds 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.
Russian President Vladimir Putin arrived in Kemerovo earlier and blamed "criminal negligence" for the blaze on Sunday.
Relatives said as many as 85 people were still missing, most of them children, according to Interfax news agency.
As well as those killed or missing, 11 injured victims were being treated in hospital, suffering from smoke inhalation.
Investigators said 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 was not yet known, but Russia's Investigative Committee had spoken of "serious violations" at the Winter Cherry mall.
However, five people have been arrested including the official suspected of deactivating the public address system.
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, at least seven hours into the protest, 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.
Mr 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 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, national broadcaster Rossiya 24 TV reported an electrical fault was the most likely cause, as in previous deadly fires in Russia.
Officials said 56 bodies had been recovered and the remains of 21 had been released to relatives for burial.
Kemerovo lies about 3600km east of Moscow.
The shopping centre, covering 23,000 sqm, opened in 2013. It includes a petting zoo, all of whose animals are reported to have died.