There were no immediate reports of casualties or the cause of incident, with an official saying the blaze had engulfed the building's exterior facade.
State TV said the area around the Gandhi Hospital in northern Tehran has been cordoned off and the hospital was being evacuated.
Pedram Pak-Ayin, the spokesperson for the Health Ministry, said that "none" of the workers and patients at Gandhi Hospital have been harmed.
He added that the cause of the fire is not clear and added, "The patients of Gandhi Hospital are being transferred to other medical centers."
According to Deputy Health Minister Saeed Karimi, 80 patients have been transferred from Gandhi Hospital to surrounding medical centers.
Tehran Fire Department spokesperson Jalal Malaki said the fire started at 1900 local time (1530 GMT) and firefighters had been dispatched to the area.
"Initial reports indicate that the fire primarily affected the exterior of the hospital building," Maleki told state TV.
No exact information has been released about the number of patients and other people inside the hospital at the time of the fire.
Comment: Whilst accidents and incompetence can be to blame, the number of buildings and factories exploding and bursting into flames, across the planet, is rather suspect; more so when they occur in countries, such as Iran, which is known to be subject to relentless, covert, attacks by nefarious agencies: Iran arrests another Mossad network, allegedly thwarting planned terrorist operations
See also: