Another 150 people were injured in the fire at the wedding hall. The fireworks set cladding alight and the building was ablaze within two minutes.
The owner of the hall has been arrested after he fled the town, said Gen Abdullah Al Jubouri, commander of Nineveh Operations, which oversees the province's security.
Thirteen people have been arrested, local media reported.
“We suspect they [those arrested] are responsible for the fire, including the owner of the event hall,” Gen Al Jubouri said.
The Iraqi official said at least 1,000 people had attended the wedding.
Iraqi Prime Minister Mohammed Shia Al Sudani has ordered the immediate formation of a committee to investigate the blaze.
A survivor of the fire said people inside the hall rushed for the exits after the fire broke out.
“We are shocked at what has happened, my daughter is in the ICU in one of the hospitals in Erbil,” said Nabil Hannu, a resident of Qaraqosh, near Mosul, who attended the wedding.
“I managed to escape. We were close to the entrance, so when the fire broke out, we were with our relatives and everyone started running. I ran with my wife and son.
“The fireworks that were lit during the event caused the fire, it managed to catch on to the ceiling of the hall which was made out of plastic. The hall managed to catch fire within seconds."
The electricity went out immediately after the fire.
Interior Ministry spokesman Gen Saad Maan said in a video from the scene that the preliminary report indicated that there was no criminal act.
“The absence of safety and security measures plus using fireworks led to the accident,” Mr Maan said.
“The burn injuries are complex and require specialised medical treatment and efforts.”
Security forces and residents in Nineveh rushed to the hospitals to donate blood.
Arrest warrants have been issued against the four owners of the hall, he added.
'Like a nightmare'
“It's like a nightmare,” resident Lena Khaled told The National.
Ms Khaled and her mother, a nurse, tended to victims at a hospital in the nearby village of Bartella.
“I don't know how to describe seeing people who have lost their whole families. There are so many dead,” she said.
“Our happiness has died … They are still bringing out bodies from the hall, there are a lot of dead children.”
Iraq's President Abdul Latif Rashid extended his condolences to the grieved families, calling the incident a “painful tragedy” and asking for an investigation.
“The incident has deeply saddened our hearts and the hearts of all Iraqis," he said.
“We emphasise the necessity of conducting an investigation to determine the circumstances of the incident and taking all safety measures to prevent its recurrence.
“Our heartful condolences go out to the families of the victims, and we wish speedy recovery to the injured.”
Iraqi Prime Minister Mohammed Shia Al Sudani declared a three-day mourning period nationwide.
The majority of the wounded are in a serious condition, the Erbil-based Rudaw quoted health officials as saying.
“No one has so far been discharged [from hospital],” said Ahmed Dubardani, deputy head of the Nineveh health directorate.
“The majority of them were completely burnt … some others had 50 to 60 per cent burns.”
Ali Qasim, an anaesthetist at Qaraqosh general hospital, spent all night treating victims and said people were walking “like zombies” around the hospital.
“Most of the dead are children. I spent an hour working on a 14-year-old girl, but she died,” he told The National.
"Every house in Qaraqosh has lost someone."
He said most people who arrived at the hospital died and the few survivors suffered “deep burns”.
“It was one of the worst days of my life when I saw people dying in front of me in this way," he said.
"I was unable to save many people. I hated being one of the medical staff, because of what I saw. I don't want to go back to hospital again."
The Governor of Nineveh, Najim Al Jabouri, announced a one-week mourning period and a one-minute moment of silence on Thursday.
Also known as Al Hamdaniyah, Qaraqosh is a predominantly Assyrian town located on the Nineveh plains between Erbil and Mosul.
It was taken over by ISIS in 2014 as the terror group swept across northern Iraq, sending many residents to flee to Erbil and the semi-autonomous Kurdish region.
Video from a Reuters correspondent at the site showed firefighters clambering over the charred wreckage of the building in search of survivors.
Ms Khaled said the lights went out as soon as the fire started, meaning many couldn't escape.
Those that did survive, she said, escaped through the kitchen.
“The main door wouldn't open, people couldn't get out. People had to come with a tractor and demolish the wall so people could escape.”
Civil defence officials quoted by INA described the wedding hall's exterior as decorated with highly flammable cladding that is illegal in the country.
“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 the fire breaks out,” civil defence said.
It was not immediately clear why authorities in Iraq allowed the cladding to be used in the hall, although corruption and mismanagement remains endemic throughout the country.
Deadly fires have killed hundreds of people across Iraq in recent years, from hospitals to displacement camps where thousands live in highly flammable tents.
In 2021, 92 people died after a fire at a hospital treating coronavirus patients in Nasiriyah.
Ambulances and medical crews were sent to the site by federal Iraqi authorities and those in the Kurdistan region, official statements said.
The Iraqi health ministry has sent medical supplies to hospitals in Nineveh, publishing images of boxes of emergency aid arriving in the governorate.
Emergency departments at hospitals in Saladdin and Kirkuk are also on standby to receive victims, while social media footage showed waiting rooms crowded with people arriving to donate blood.