At least 113 people were killed and 150 others were injured when a fire gutted a wedding hall in Hamdaniyah, a town east of Mosul, authorities said Wednesday.
Indoor fireworks were cited as the likely cause for the blaze that sparked a panicked stampede for the exits.
More than 150 people were injured by the flames, the choking smoke, or in the crush to flee the reception hall, which was reduced to charred debris and piles of twisted furniture under a partially collapsed ceiling.
"I thought there had been an explosion," said Martin Idriss, 19, who was working in the kitchen when the fire broke out Tuesday evening in the venue in the mainly Christian northern town of Qaraqosh.
"The flames were devouring the whole hall," he said.
"When I went back in, I saw the charred bodies of three children," he said, adding that the venue's emergency exits had proved "inadequate" for the hundreds of guests trying to escape.
Early reports and unverified video footage online suggested that flares shot up sparkling flames that ignited ceiling decorations before the fire engulfed highly flammable construction materials.
Health authorities "counted 100 dead and more than 150 injured in the fire at a marriage hall in Hamdaniyah," Iraq's official INA news agency reported in what it called a "preliminary tally."
The casualty toll was confirmed to Agence France-Presse (AFP) by Health Ministry spokesman Saif al-Badr, who said most of the injured were being treated for burns, oxygen deprivation and crush injuries sustained in the struggle to escape.
The Iraqi Red Crescent reported more than 450 casualties, without providing a breakdown of deaths and injuries.
Wedding guest Rania Waad, 17, who sustained burns to her hand, said that as the bride and groom "were slow dancing, the fireworks (flames) started to climb to the ceiling (and) the whole hall went up in flames."
"We couldn't see anything," she said, choking back sobs. "We were suffocating, we didn't know how to get out."
At the town's main hospital, an AFP photographer saw ambulances with sirens blaring and dozens of people gathering to donate blood, while black body bags were being loaded onto a refrigerated truck.
Early on Wednesday, police and firefighters were still sifting through the charred remains of the reception hall where mangled metal chairs lay strewn amid the debris.
Civil defense authorities said the hall had been fitted with prefabricated panels that were "highly flammable and contravened safety standards."
The danger was compounded by the "release of toxic gases linked to the combustion of the panels", which contained plastic, they said in a statement.
"Preliminary information" suggested indoor fireworks had ignited the blaze, they said.
Nine of the venue's staff were arrested and four arrest warrants were issued for its owners, Interior Ministry spokesperson, General Saad Maan said.
Iraqi Prime Minister Mohammed S. Al Sudani declared three days of national mourning.
He also ordered "intensified periodic inspections" of entertainment venues nationwide to "ensure that safety measures are followed" and to "identify any non-compliant buildings."
Safety standards in Iraq's construction sector are often disregarded, and the country, whose infrastructure is in disrepair after decades of conflict, is often the scene of fatal fires and accidents.
In July 2021, a fire in a hospital COVID-19 unit killed more than 90 people in southern Iraq.
And in April of the same year, oxygen tanks exploded and triggered a fire at a Baghdad hospital also treating COVID patients, killing more than 80 people.
