Forest guards heard gun shots in the western Burapahar range of the park late last night following which an operation was launched in the area.
An encounter followed but the poachers managed to escape, the officials said.
During search operations, the forest guards came upon the carcass of two rhinos near Dirang forest camp of the range, about 20 metres away from National Highway 37.
The poachers managed to escape with the horn of one of the rhinos, they said.
One person, identified as Naren Singh, was arrested and efforts were on to apprehend the poachers who were suspected to be six in number, the officials added.
