According to Russia's state-run TASS News Agency, a column of black smoke was seen above the building's section housing a store of OBI, a retail chain of home improvement supplies.
"At present, the entire building is ablaze, the fire has spread to around 18,000 square meters," a rescue source told TASS.
According to an emergency worker, a short circuit might have caused the blaze.
"An explosion caused the fire to spread," the worker said.
The exact reason will be ascertained in a probe to be conducted after the blaze is put out.
There were no immediate information on casualties or injuries.
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