Tehran(CNN) Emergency workers have dug tunnels into the wreckage of a collapsed high-rise in downtown Tehran in their search for survivors and bodies, Iranian state TV reported.
They have not yet found any of the firefighters believed to be buried under the rubble, Iran's fire chief told the official Islamic Republic of Iran News Network. More than 20 are thought to have died.
The two tunnels lead from adjacent buildings into the collapsed 17-story Plasco building, IRINN reported. The huge size of the site makes reaching the trapped firefighters very difficult, the station said.
Iran's Supreme Leader, Ayatollah Ali Khamenei, issued a statement Thursday supporting the firefighters' rescue efforts and giving his condolences to the families of the firemen who died.
Tehran building collapses following huge fire inside
The rubble of the Plasco building in Tehran, Iran, is seen after it collapsed following a fire on Thursday, January 19. As many as 30 firefighters are feared dead, according to Iran's semi-official Fars news agency. Official news agency IRNA cited the head of Tehran Emergency Services as saying 70 people were injured in the fire.
Iranian firefighters comfort a fellow fireman in the aftermath of the building collapse.
Emergency crews continue operations after the collapse of the Plasco building. Built more than 50 years ago, the iconic building was home to hundreds of garment manufacturers and other businesses, Fars reported.
A firefighter climbs over the fallen wreckage of the Plasco building. Thirty-five firefighters are missing after the multi-story building collapsed around them as they battled a blaze, Tehran Fire Department spokesman Jalal Maleki told a local journalist on the scene. Rescue teams are trying to dig out the missing firefighters, Maleki said.
Authorities surround the debris of the collapsed building, which was one of Tehran's oldest high-rises.
A firefighter reacts outside the building, where the blaze burned through the upper stories for more than three hours before the structure came down.
Firefighters outside the building before it collapsed.
Firefighters worked to move people away and clear the area before the building collapsed.
Iranians watch as firefighters work to extinguish the blazing Plasco building.
Firefighters work to control the blaze. Fars agency cited Mojtaba Doroodian, head of the shirt makers' union, as saying that the fire was the result of a leak in a small gas cylinder on the 10th floor, which caused an explosion when a merchant turned on the lights in his store. Tehran Fire Department spokesman Jalal Maleki said the cause of the building fire and collapse is being investigated.
Fire crews attempt to extinguish the blaze.
Residents take photos of the Plasco building engulfed in smoke and flames.
People watch as smoke rises from the windows of the Plasco building.
"More than 20 of our colleagues in the fire department have lost their lives while trying to save the people in the fire," Tehran mayor Mohammad Baqer Ghalibaf was cited by IRINN as saying Thursday.
Earlier Thursday, Tehran's fire department spokesman Jalal Maleki told IRINN an estimated 20 to 30 firefighters were on the third floor of the Plasco building when it collapsed.
The cause of the fire and collapse is being investigated, he added.
Housing garment manufacturers and other businesses, the Plasco building was one of Tehran's oldest high-rises and a feature of the city's skyline.
The commercial building's dramatic collapse on live TV came after a fire raged for hours through its upper floors.
Official news agency IRNA cited Foreign Ministry spokesman Bahram Qasemi as saying Friday that all necessary measures had been taken to secure the German, Turkish and British embassies nearby.
Located on Jomhouri Avenue in central Tehran, the Plasco building was constructed in 1962. It was named after a successful plastics business, Plascokar.
Seventeen stories tall, it was the country's first private high-rise building and soon became a well-known feature of the city's skyline.
CNN's Shirzad Bozorgmehr reported from Tehran and Laura Smith-Spark wrote and reported from London. CNN's Sara Mazloumsaki contributed to this report.