An explosion at about 9 a.m. local time caused the fire in the oil sludge processing shop at the plant in Khanty-Mansi Autonomous Area, ITAR-Tass reported.
The injured were taken to the region's central clinic in Khanty-Mansiisk, a source with the Russian Investigative Committee said.
The plant is owned by Invest Oil, RIA Novosti reported.
The fire occurred in two metal hangars and may have been caused by gas, authorities said.
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