At least 20 firefighters have died and dozens more are trapped under the rubble after Iran's oldest high-rise collapsed on Thursday following a fire, Iran's state Press TV reported.
"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."
Tenants in the building, dating from the early 1960s, include a shopping centre and clothing workshops.
Fire danger to historic building
Iranian state television said 200 firefighters were called to the scene to battle the blaze before the building collapsed.
Images showed flames pouring out of the top floors before the building crumbled to the ground.
"We had repeatedly warned the building managers about the lack of safety of the building," fire brigade spokesman Jalal Malekias said, adding that it lacked fire extinguishers.
"Even in the stairwells, a lot of clothing is stored and this is against safety standards. The managers didn't pay attention to the warnings," he said.
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The Plasco building was the first high-rise and shopping centre in Tehran. It was the city's tallest building when it was finished in 1962, before being dwarfed by the construction boom of later years.
It was built by Habibollah Elghanian, a prominent Iranian-Jewish businessman who was arrested for ties to Israel and sentenced to death and executed after the 1979 revolution.