At least 43 people were killed Sunday in a devastating fire that ripped through a bag factory in the cramped, congested old quarter of the Indian capital New Delhi, trapping scores of workers who were sleeping inside.

The blaze was the worst in Delhi since 59 movie-goers died in a cinema in 1997, with the city's poor planning and enforcement of building and safety regulations often responsible for such deadly incidents.

Tearful relatives spoke of receiving desperate calls from factory workers from around 5:00am (23:30 GMT) pleading to be freed from the inferno in the dark, poorly lit premises in the commercial hub of Sadar Bazar.

The four-storey building was home to a series of manufacturing units producing items including schools bags and packing materials which only worsened the spread of the fire, officials said. Locals said the factory also made purses.

"Most of the casualties happened because of suffocation," witness Mohammed Khalil told AFP. "After the fire, people didn't have any way to get out and I believe many were asleep and because of the smoke, they got suffocated."

Outside a nearby hospital morgue, anxious relatives and friends gathered to identify the bodies.

Naushad Ahmad, was desperately looking for his friend who remained missing, unable to reach him on his mobile phone. "I have been to the factory and this tragedy was waiting to happen," he told AFP.

"There was only one exit and entrance to the building, with all the electricity meters installed at the main door. People didn't get a chance to escape."