Iran's oldest high-rise in southern Tehran collapsed on Thursday following a major fire in the building, leaving dozens of people injured.
The 17-story structure crumbled after the fire engulfed the top floors of the building in downtown Tehran as scores of firefighters battled the blaze.
The Fars news agency and the IRIB news website said at least 30 firefighters were feared to have been killed in the incident but officials did not confirm any deaths.
The head of Tehran's emergency services told IRIB that at least 70 people have been injured and 23 hospitalized.
Tehran Mayor Mohammad Baqer Qalibaf said between 20 to 25 people are believed to have been trapped under the rubble.
Fars said a firefighter had texted a message to a colleague, saying he was alive and trapped with several others at the building's engine room.
Officials have not given the exact number of casualties so far.
Firefighters battled the blaze for several hours before the collapse as police kept out shopkeepers and others trying to rush back in to collect their valuables.
Reacting to the incident, Iranian President Hassan Rouhani tasked the Interior Ministry with launching an immediate investigation into the causes of the tragedy.
"The causes of this incident and those responsible must be determined in the shortest possible time and reported, and every necessary measure must be taken by concerned institutions to attend to the injured and compensate the losses incurred by those damaged in the incident,” Rouhani said.
Vice President Es’haq Jahangiri and Health Minister Hassan Ghazizadeh Hashemi have also visited the site.
"The administration stands by the nation, and all relevant bodies have been mobilized to save the injured,” Jahanigiri told reporters.
Ghazizadeh Hashemi, for his part, said all hospitals and medical emergency centers in the capital were on high alert and fully prepared to provide aid to those wounded in the blaze and the ensuing building collapse.
Meanwhile, Mohsen Hamedani, a security official with Tehran Governor General's Office, said initial investigations suggest that the fire had been caused by a short circuit in the electrical system of the building, Tasnim news agency reported.
"Reports that the blaze was of a security nature are not correct and the incident was the result of totally natural causes," he added.
The building came down at around 11:30 a.m. local time (0800 GMT), which was shown live on state television.
A side of the building buckled first, tumbling close to a firefighter perched on a ladder and spraying water on the blaze.
Nearby buildings including the embassies of Turkey, Germany and the UK have been evacuated. Authorities at Tehran's governor's office have ruled out terrorism, Presstv reported.
The tower was inaugurated in 1962 and named after a plastics manufacturing company. It was the tallest building in the city at the time of its construction. It included shopping centers and clothing workshops.