Additional Deputy Commissioner K Nongbri said at least one person has died in the accident which took place at about midnight in the accident-prone stretch of NH 44 at Ratacherra area.
He said the 25 injured were rushed to a hospital.
The night bus from Guwahati was bound for Tripura and police and fire personnel have rushed to the accident site, he said.
The firemen's help is being taken to pull out the bus from the gorge.
NH 44 is the only national highway that links Agartala with the rest of the seven NE states.