Soldiers, sniffer dogs and rescue workers were searching the ruins of the Plasco building after it crashed down in a giant cloud of dust. The collapse was shown live on state television and one witness described it as "like a horror movie".
"At least 20 firefighters who were trapped under rubble have died," Mayor Mohammad Baqer Qalibaf said. "They are martyrs. They lost their lives when trying to help people."
But Tehran Fire Department spokesman Jalal Maleki told the broadcaster: "I cannot confirm the death of around 20 firefighters ... but some of them have been killed. The rescue operation continues."
Tehran’s Governor Hossein Hashemi told state TV rescue workers were opening three separate routes to access those trapped.
"One of those trapped in the building sent a text message saying five of them are alive," judiciary website Mizan reported.
State TV said at least 88 people, including 45 firefighters, were injured. Most were taken to hospital and many quickly discharged, it said.
The semi-official Tasnim news agency said troops had been sent to help dig through the ruins. It said one of the first firefighters to be reached had asked to be let back inside to save his colleagues.
The agency quoted an official in the Tehran governor's office as saying an electrical short-circuit had caused the fire, but there was no immediate confirmation of this.
Supreme Leader Ayatollah Ali Khamenei and President Hassan Rouhani sent condolences to the families of those killed. Rouhani ordered an investigation and compensation for those affected, state TV reported.
Occupants of the building had been evacuated as firefighters tackled the blaze. State TV said the tenants included garment manufacturers, and it broadcast footage of business owners trying to re-enter the wreckage.
"I have lost everything. What am I going to do now. What should I tell my family?" owner of one of the 400 business units in the building, Mohsen Ghamisi, told Reuters by telephone.
Tasnim news agency reported that the business units and shops inside the building were not insured because of a lack of required safety measures.
Sniffer dogs searched for survivors buried under giant slabs of concrete and heaps of twisted metal. The rescue operation could last more than two days, state TV said.
The Plasco building, Iran's first private high-rise, was built more than 50 years ago by an Iranian-Jewish businessman who was arrested and sentenced to death for ties to Israel after the 1979 Islamic revolution.
Maleki said: "We had repeatedly warned the building managers about the lack of safety."
The owner of a nearby grocery store, forced by police to leave the area, told Reuters by telephone: "It was like a horror movie. The building collapsed in front of me."
The semi-official Fars news agency said police had cordoned off the nearby British, German and Turkish embassies.
"The embassies are being protected by diplomatic police forces... All the security and safety measures have been taken," TV quoted Foreign Ministry spokesman Bahram Ghasemi as saying.
Banner/Thumbnail Photo Credit: Reuters