DHAKA (AFP) - Bangladesh police on Saturday (July 10) arrested for murder the owner of a factory where 52 people died in an inferno, as it emerged that children as young as 11 had been working there.

Police said Abul Hashem and four of his sons were among eight people detained over the inferno, which broke out on Thursday and raged for more than a day.

A separate inquiry has been launched into the use of child labour at the facility.

Mr Jayedul Alam, police chief for Narayanganj district where the factory is located, said the entrance had been padlocked at the time of the blaze and the factory breached multiple fire and safety regulations.

"It was a deliberate murder," the police chief told Agence France-Presse.

Before his arrest, Hashem told the Daily Star newspaper the fire "may have been a result of workers' carelessness" and a discarded cigarette could have sparked the carnage.

Emergency services found 48 of the bodies on the third floor of the Hashem Food and Beverage factory in Rupganj, an industrial town outside the capital Dhaka.

A fire services spokesman said the exit door to the main staircase had been padlocked. Highly flammable chemicals and plastics had also been stored in the building.

Ms Laizu Begum, who spent hours waiting outside the factory for news of her 11-year-old nephew, said he had been working on the third floor.

"We heard the door of the floor where my nephew worked was padlocked. Then we realised after seeing how big the fire was that he is probably dead," she said.

Outside the burned shell of the factory and at the hospital morgue, AFP spoke to 30 survivors and relatives of the dead, who said child workers at the factory were paid just 20 taka ($0.32) per hour.

Ms Bilal Hossain, whose 14-year-old daughter was among the missing, went to the Dhaka Medical College Hospital morgue with a photo, begging police and doctors to find her remains.

"I sent my baby girl to die," said Ms Hossain, who added that the company owed the girl back wages. "How will I tell her mother?"

Mr Chandu Mia held a photo of his 15-year-old daughter. "I am not sure if she is alive," he said, holding back tears.

State Minister for Labour Monnujan Sufian said inquiries had begun into the use of child workers at the factory.

She said that she had spoken at a hospital to two survivors aged 14.

"I went to the hospital and I asked them how old they are. The youngest were 14," she said.

Ms Sufian said some children aged 14 were allowed to work in non-hazardous jobs, but that the Hashem factory was considered hazardous.

"If child labour is proved, we will take action against the owner and the inspectors," she said.

Bangladesh pledged reforms after the Rana Plaza disaster in 2013. More than 1,100 people were killed after the complex collapsed.

But there have been a series of fires and other disasters since then.

In February 2019, at least 70 people died when a fire ripped through Dhaka apartments where chemicals were illegally stored.

Unions have said the latest disaster has again showed how labour and factory laws are poorly enforced.

The International Labour Organisation (ILO), a UN agency, said the blaze "illustrates the urgent need" for Bangladesh authorities and building owners to ensure that factories meet national safety standards.

The ILO said the government must "apply renewed vigour in addressing the safety deficits in workplaces across the country".