Up to 30 people, all of them most likely firefighters, are believed trapped under the rubble of the Plasco building, a 54-year-old high-rise which collapsed on Thursday morning.
Two firemen have so far been confirmed to have died in the incident.
Rescuers have been using life detection devices to locate possible survivors, and at least four responses have been picked up, likely indicating that at least four people are still alive.
Turkish President Recep Tayyip Erdogan, Pakistani Prime Minister Nawaz Sharif, Syrian President Bashar al-Assad, and Tajikistan President Emomali Rahmon are among the leaders who have sent messages of condolences over the incident.
Firefighters from different countries have also expressed sympathy to the families of the Iranian firefighters who lost their lives in the tragic event.
They, including firemen from Venezuela, Britain, the US, Ireland and Turkey, praised the courageous Iranian firefighters who sacrificed their lives to put out the fire.
The Iranian administration has declared Saturday as a day of national morning for those killed in the building collapse.
All Iranian embassies and consulate-generals abroad have been ordered to fly the flag at half-mast in honor of firefighters who lost their lives to save others.
On Saturday morning, Iran’s President Hassan Rouhani visited the site of the collapsed Plasco building.
Speaking to reporters, Rouhani stressed that the search and rescue operation should continue until all those trapped under the rubble are saved.
The Plasco building was Iran’s oldest high-rise. Rising 17 stories above the ground, it had been built in the early 1960s and was the country’s tallest building at the time of construction.
Rouhani also touched on the need for "comprehensive plans” to renovate old structures across the country and said, "We can get entrepreneurs, investors, and banks onboard to help renovate these buildings… The plan is underway and it needs to be precipitated.”
The Iranian president was accompanied in the visit by several ministers, advisers, and other senior officials.