(CNN) -- At least 43 people have died in a major blaze that broke out in a factory in India's capital New Delhi, police and fire department officials told CNN.

The fire swept through the five-story building in the early hours of Sunday, as laborers and factory workers were asleep inside. Some died due to asphyxiation, officials said.

"The problem was the smoke -- all the windows and doors were shut and there was dense smoke inside," said Sunil Choudhary, deputy chief fire officer.

"No one could get out. There was an iron door and it was locked and people were brought out only after we broke the door open. It had become a toxic chamber."

India Fire

People wait to identify and collect bodies of relatives who died in a fire in New Delhi, India, Sunday, Dec. 8, 2019. Dozens of people died on Sunday in a devastating fire at a building in a crowded grains market area in central New Delhi, police said. (AP Photo/Manish Swarup)

An eyewitness said some workers had tried to escape from a terrace, but it was locked.

"There are no proper ways to climb or get down, there is no fire safety, there is nothing," Mohammad Samar said, adding that this was not the first blaze at the site, which was a plastic factory that manufactured toys.

Samar said a number of small, unauthorized factories had been renting out space in the building, and that the complete lack of safety provisions was widely known.

Another eyewitness, who helped with rescue efforts, said he had seen boys trying to escape from the factory's roof, while others desperately crowded near sealed windows.

"I saw that the boys, who were standing there on the roof, they started screaming ... calling out to me ... saying 'Mullah sir please save me,'" Mohammad Manzur said.

India Fire

A family waits to collect the body of their relative who died in a fire in New Delhi, India, Sunday, Dec. 8, 2019. Dozens of people died on Sunday in a devastating fire at a building in a crowded grains market area in central New Delhi, police said. (AP Photo/Manish Swarup)

Avtar Singh, an assistant division officer for the fire department, said that more than 60 people had been evacuated from the building and the injured were transported to three local hospitals.

Fire officials said they had struggled to reach the factory in the city's old quarter, a tangle of narrow, busy lanes lined with manufacturing units.

Thirty fire engines were stationed near the site, but only one managed to get to the building and extinguish the blaze through a relay system, Singh said.

The fire, which officials say was sparked by an electrical fault, took almost three hours to put out.

India Fire

The walls of a building stand blackened after it caught fire in New Delhi, India, Sunday, Dec. 8, 2019. Dozens of people died on Sunday in a devastating fire at a building in a crowded grains market area in central New Delhi, police said. Firefighters fought the blaze from 100 meters (yards) away because it broke out in one of the area's many alleyways, tangled in electrical wire and too narrow for vehicles to access, authorities at the scene said. (AP Photo/Dinesh Joshi)

Indian Prime Minister Narendra Modi called the fire "extremely horrific" in a statement on Twitter.

"My thoughts are with those who lost their loved ones," Modi said. "Wishing the injured a quick recovery. Authorities are providing all possible assistance at the site of the tragedy."

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