"Serious violations [of the law] took place when the mall was being built and when it was functioning. The fire exits were blocked," Svetlana Petrenko, a spokeswoman for the committee, said in a statement.

She said investigators, who have opened a criminal investigation into the blaze, were looking into other possible violations. Four people have already been detained, including the owners and lessees of outlets inside the mall.

Emergency services said they had extinguished the fire, but later said it had reignited in places, and that rescuers were struggling to recover bodies beneath smouldering rubble.

It was unclear if any people were still unaccounted for. Veronika Skortsova, the health minister, said from the scene that 11 people were in hospital, including an 11-year-old boy who was in a serious condition. Russian media said the boy had leapt from a window and that both his parents had been killed.

An unofficial list of those missing circulating on Russian media included more than 20 children, some as young as five. Mobile phone messages sent from one of those on the list, 13-year-old Maria Moroz, and published by Russian media, said:

"We are burning. I love you all. This is perhaps farewell."

Alexander Lillevyali told online newspaper Meduza that he and his wife Olga had lost all three of their daughters, two of them aged 11 and one aged five, in the blaze.

He was cited as saying he had dropped off his daughters at the cinema and that one of them had phoned later to say the auditorium was filling with smoke and that they couldn't get out because the doors were locked.

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He described how he had led rescuers up the stairs, but that they had been ordered to go elsewhere and that rescuers, citing rules, had refused to give him a respiratory mask.

"My daughters were left to burn because of their bloody rules," Lillevyali told Meduza.

Witnesses told Russian media the fire alarm and sprinklers had failed to function and that many people had found themselves trapped because exit doors were locked.

Video footage from inside the mall after the fire broke out showed a group of people in a smoke-filled staircase trying to smash a fire exit door, which was jammed.

Reuters