No injuries have been immediately reported.
The fire broke out today at the Plasco building, built over 50 years ago. Police have blocked off streets around the 17-story structure, which was among the first high-rises built in the Iranian capital.
Jalal Maleki, a fire department spokesman, told Iranian state television that 10 firehouses responded to the blaze, which was first reported around 8 am.
Maleki says the fire is now under control as firefighters struggle to extinguish the blaze.