Hundreds were celebrating in a banqueting hall in Qaraqosh in Nineveh province when it happened.
It is not known what started the fire but some reports suggest fireworks set it off.
Flammable panels fuelled the flames, causing parts of the ceiling to catch fire and fall, fire officials said.
“The fire led to the collapse of parts of the hall as a result of the use of highly flammable, low-cost building materials that collapse within minutes when fire breaks out,” Iraq’s civil defence directorate said, quoted by state news agency INA.
It was not immediately clear if the bride and the groom were among the victims.
Footage posted online showed the couple on the dance floor before flaming chunks begin falling onto the dance floor.
Firefighters could be seen climbing over the wreckage of the building in search of survivors on Wednesday morning.
Eyewitnesses said hundreds of people had been in the venue when it caught fire at around 22:45 local time (19:45 GMT) on Tuesday.
“We saw the fire pulsating, coming out of the hall. Those who managed got out and those who didn’t got stuck. Even those who made their way out were broken,” Imad Yohana, a 34-year-old who escaped the inferno, told Reuters.
Another wedding guest, Rania Waad, who sustained a burn to her hand, said that as the bride and groom were slow dancing “fireworks started to climb to the ceiling, the whole hall went up in flames”.
“We couldn’t see anything,” the 17-year-old told news agency AFP. “We were suffocating, we didn’t know how to get out.”
Another survivor said several members of his family were among the victims.
“When it [the fire] happened my mother was in the bathroom,” he said.
“I couldn’t find her after. I searched for my daughter, my son, my wife, my father and I couldn’t find them. They are gone.”
Iraq’s president posted on X, formerly known as Twitter, that he had told officials to “mobilise all efforts to provide relief to those affected by the unfortunate incident”.
Meanwhile, Iraqi Prime Minister Mohammed Shia al-Sudani said building inspections would be carried out and safety procedures would be scrutinised, with “the relevant authorities held accountable for any negligence”.
He also declared three days of national mourning.
The number of reported victims is unclear. The deputy governor of Nineveh, Hassan al-Allaq, told Reuters that 113 people had been confirmed dead, while the Red Crescent humanitarian group put the total number of dead and injured at nearly 450.
The regional governor told INA the number of deaths and injuries could rise.
The injured have been transferred to hospitals across the Nineveh region. At the main hospital in Qaraqosh, which is about 15km (9 miles) east of the region’s capital Mosul, dozens of people arrived to donate blood to help the injured. Qaraqosh is also known as al-Hamdaniya and Bakhdida in Iraq.
An Iraqi journalist in the city of Erbil, where victims are also being treated, told the BBC there were not sufficient “logistical tools to rescue the people” and that Mosul did not have enough ambulances, staff and medical equipment.
“Local officials of Mosul, they all blame the Iraqi government because they didn’t solve the problem of hospitals, and generally, the problem of health sector in Mosul after the ISIS (Islamic State group) occupation of the city,” added Blesa Shaways.
Mosul was liberated from three years of IS rule in 2017 following a brutal fight that left the city in ruins.
Some media reports have said the couple held a Christian wedding, though this has not been confirmed.
Qaraqosh was the biggest Christian town in Iraq before it was overrun by IS in 2014 and most people fled from persecution.
IS militants committed many atrocities against the Christians who remained before the group was driven out by Iraqi and US-led coalition forces in 2016 and more than 2,000 homes were reportedly burned to the ground.
About half of Qaraqosh’s residents are said to have returned since the town was liberated but many of the destroyed homes have yet to be rebuilt.
Such incidents are not rare in Iraq – where corruption and mismanagement are rife and accountability is lacking.
In 2021, officials said a lack of safety measures had contributed to the deaths of nearly 100 people in a fire at a hospital in the city of Nasiriya.
