President Vladimir Putin flew to the Siberian city of Kemerovo two days after the tragedy and laid roses at a makeshift memorial as critics questioned his response to one of the deadliest fires in Russia over the past century.
Hundreds of residents meanwhile packed Kemerovo's central square, calling for the resignation of the region's veteran governor and questioning the official death toll.
The father of one of the victims told the crowd he spoke to his daughter on the phone while she was trapped inside the shopping centre.
"She cried: 'I'm here, dad, here'. I told her: 'Lie down on the floor and breathe. Breathe and don't die'."
"I cried, I was crying to my daughter. She said: 'Dad, I love you. I'm suffocating, I'm losing consciousness.'"
In Moscow, around 2,000 people gathered on Pushkin Square in mourning on Tuesday evening, leaving flowers, lighting candles in the shape of the word "Kemerovo" and letting off white balloons.
People lay flowers in Moscow for the victims of a fire in a shopping centre in Kamerovo. Source: AAP
Russia's main opposition leader Alexei Navalny and his wife left a bunch of red carnations.
Some protesters in Moscow shouted slogans calling for the sacking of Kemerovo's region and for "Russia without Putin."
Protester Yekaterina Nekrasnova, a 29-year-old photographer, said: "My friend in Kemerovo has lost two children and her husband is in intensive care."
She blamed the fire on "negligence and greed."
In Saint Petersburg, Russia's second largest city, hundreds gathered on the central Marsovo Polye square, many carrying flowers.
"All these children were killed by corruption and lawlessness. These ruling powers killed them," said 26-year-old Varvara Mikhailova.
Russian President Vladimir Putin listens to locals and relatives of the victims of the fire. Source: AAP
Investigators said relatives had reported a total of 67 people missing, while the official toll has been given as 64.
After a huge outpouring of grief and anger on social media, the Kremlin announced a nationwide day of mourning for Wednesday for victims of the fire, which ripped through the busy shopping centre on Sunday afternoon.
"My family is no more," Igor Vostrikov - who lost his wife, sister and three children aged two, five and seven years - said on VKontakte, Russia's version of Facebook.
"The ruling regime in my country is to blame for it."
Investigators said the victims were burned alive or suffocated because emergency exits were locked, notably in a cinema where children watched cartoons.
A criminal probe has been opened and five people have been arrested over the blaze.
Multiple safety rules were violated, the fire alarm system had not worked since last week and staff did not follow correct emergency procedures, officials said.
'We are dying. I love you'
Putin, who was re-elected for a fourth term in polls earlier this month, visited a memorial of toys, flowers and balloons near the gutted mall's facade, telling officials he felt "like wailing" over the number of victims.
"What is happening here? These are not armed hostilities. This is not an unexpected release of methane in a mine. People, children came to relax," Putin said.
"We are talking about demographics but are losing so many people. Because of what? Because of some criminal negligence, slovenliness," Putin said.
Sixty-four people, including 41 children, have died in a Siberian mall fire. Source: AAP
Russian newspapers ran heart-wrenching accounts of children's last minute calls to their parents and relatives.
"Tell my mom that I loved her," one woman quoted her niece as saying in comments in the Komsomolskaya Pravda newspaper.
Vostrikov, who lost his family in the blaze, said he had spoken to his wife in her final moments.
"We have been locked inside the movie theatre. We are suffocating, we are dying. I love you," he said she had told him.
Speaking in videotaped comments, he claimed the number of victims was much higher than reported.
Many others also questioned the official death toll but officials said the figures were final, urging Russians not to trust unconfirmed reports on social media.
The head of Russia's Investigative Committee, Alexander Bastrykin, said ticket collectors and other staff fled the scene, leaving movie-goers locked inside.
"Those workers who were supposed to be in charge of safety, organising evacuation, they were the first to flee," he told Putin.
Bastrykin also told Putin that a teacher had left a whole class of children alone in a games room while she shopped.
Mourners hold portraits of their dead relatives as they call for the resignation of the region's governor. Source: AAP
'Gas chambers'
Temperatures during the blaze reached 600 degrees Celsius and some of the bodies were so badly burned they would need to be identified through DNA testing, officials said.
Meeting with a group of grieving locals, Putin said some 100 investigators were working at the scene.
A young man told Putin he was outraged that the doors were locked at the mall, effectively turning the premises into "gas chambers".
Putin promised a "transparent" investigation but declined to fire Aman Tuleyev, who has been governor of the Kemerovo region for the past 21 years.
Tuleyev apologised to Putin over the rally, calling its organisers troublemakers.
The Russian leader also visited victims at a hospital including Ivan Zavarzin, 18, who survived the fire after jumping from the top floor.
