Investigators said the blaze engulfed an area covering 3,000 square metres in the factory situated in the city's east.
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"The bodies of 11 people were recovered when the fire was put out," the local branch of the Investigative Committee said in a statement.
The fire broke out at around 1800 GMT on Saturday and was only extinguished around five hours later, authorities said.
The cause of the blaze remains unknown. A criminal investigation was launched to determine whether it may have been caused by negligence or arson.
The emergency situations ministry initially reported that there had been no fatalities in the fire, but investigators later said that bodies had been recovered from the site.
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The victims are believed to be migrant workers, Russian news agencies reported.
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