"The fire broke out in a private-owned wooden house in the town of Troitsk at about 5.30 a.m. local time," the department said. "A large family lived in the house. There were 11 children in there at the time."
Part of the house had collapsed by the time fire fighters arrived at the scene, while the other part toppled as they were fighting the blaze. The father and one child had serious burns and were taken to hospital.
The fire fighters extinguished the fire, entered what remained of the house and started searching for five people believed to have been inside. They discovered three children's corpses.
The search effort is still underway. A special commission will investigate the fire's cause.