Divisional Forest Officer (DFO) Nand Kishor told PTI the fire broke out in Madanpur forest range of the reserve due to unspecified reason.
Forest guards on duty swung into action immediately and with normal fire fighting equipment sprinkled water to douse the flames, he said.
Kishor, who is also Deputy Director of Valmiki Tiger Project (VTP), said there was no casualty or injury to any wild animal, including tigers, in the reserve.
The DFO was earlier quoted as saying that the fire had engulfed 100 acres and many animals perished.