Thousands of people on Tuesday 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.
Several thousand people rallied outside the local government headquarters on Tuesday, demanding that officials be sacked over the fire safety shortcomings, reports BBC.
There were also some chants of "Putin resign!"
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.