A fire broke out and was extinguished at Russian steelmaker NLMK's main plant, the regional governor has said.
Lipetsk regional Governor Igor Artamonov said preliminary data showed the fire at the Novolipetsk Steel plant was caused by a drone.
He did not mention Ukraine but said there were no casualties.
Social media footage showed an explosion followed by a large orange flame.
The plant, which makes 18% of Russian steel, is about 400km from the Russia-Ukraine border.