ANKARA (Reuters) - Iranian officials said on Friday that 25 people were still unaccounted for more than 24 hours after the collapse of a 17-storey commercial building in Tehran, in addition to 20 firefighters who died in the blaze, state TV reported.

A collapsed building is seen in Tehran, Iran. Tasnim News Agency/Handout via REUTERS

One official denied that all 25 might be trapped under the rubble, saying “maybe five of those who worked in the building are trapped”, the semi-official Fars news agency reported.

“Police have received reports that 25 people are missing. We urge people to report if any of their family members that worked in the Plasco building is missing,” a police official told TV.

Thick smoke and fire has hampered the search for the bodies of the firefighters who were killed as they evacuated people from Iran’s oldest high-rise building, which housed hundreds of clothing warehouses as well as a mall and other businesses.

Fire department officials have warned of the danger of more explosions, Fars said.

Iranian media carried photos of weeping relatives and dozens of people lined up to donate blood. The government declared Saturday a day of national mourning.

“We are trying any way possible to reach them ... but very thick rising smoke is making the work very difficult,” Tehran’s emergency services head, Pir Hossein Kolivand, told state TV.

“We are dealing with fire, thick smoke and lack of oxygen.”

Round-the-clock TV coverage showed dozens of firefighters and soldiers cutting through metal girders and concrete blocks to try to retrieve the bodies, and police trying to stop people getting into the building to retrieve valuables.

“These firefighters prevented a disaster. Hundreds of people could have been killed if they had not returned to the building,” Tehran Fire Department spokesman Jalal Maleki said.

“The chance of rescuing anyone alive is almost zero.” About 88 people, including firefighters, were injured when the Plasco building caught fire and collapsed. Only three were still in hospital, state TV reported.

On Friday, Iran’s Supreme Leader Ayatollah Ali Khamenei’s representative visited wounded firefighters in hospital and President Hassan Rouhani has ordered an immediate investigation.

The building’s managers had ignored repeated warnings about poor safety standards and the building’s weak structure, Tehran’s mayor Mohammad Baqer Qalibaf said on Thursday.

Authorities said the financial damage was estimated at about $500 million, and that most of the shops and businesses were not insured because safety standards had not been met.