Jalal Maleki, a fire department spokesman, told Iranian state television that 10 fire stations responded to the blaze, which was first reported around 8 a.m. local time (11:30 p.m. ET on Wednesday).
The Plasco building consisted of a shopping centre and numerous clothing workshops. Located on Jomhoori Avenue, it was attached to a multistory shopping mall, just north of the city's vast bazaar. The 17-storey commercial building was built in 1962 and at the time was the tallest building in the city.
Mojtaba Khaledi, the spokesman for the country's emergency services, told IRNA that 84 people were injured and 33 were initially hospitalized, 23 of whom were discharged after treatment for less severe injuries. The figures on the exact number of casualties are not yet clear.
The building collapsed at 11:30 AM in a matter of seconds after flames consumed the top floors and firefighters fought to control the blaze for hours.
Firemen, soldiers and other emergency responders dug through the debris, looking for survivors. While it was not clear how many people were in the steel-and-concrete building, witnesses said many had slipped through a police cordon while the fire burned to go back inside for their belongings.
More than 200 people injured in the fire were transferred to medical facilities, IRNA news agency reported.
Hundreds of people have queued up in hospital and clinics to donate blood, while several firefighters are reported to have been trapped in the basement of the collapsed commercial complex.
Fars news agency reported that a firefighter had sent a text message to a colleague, saying he was alive and trapped with several others at the building's engine room.
Army special forces were deployed to aid the search and rescue efforts.