At least 43 people have died in India's capital New Delhi after a fire swept through a factory where workers were sleeping, police have said.

Another 16 people were being treated for burns or smoke inhalation.

More than 50 people have been moved to safety, a Delhi Fire Service official said.

The blaze broke out around 5.30am on Sunday in the six-storey building which is in a busy residential area.

The factory was making handbags and lots of raw material was stored inside the building, causing the fire to spread quickly, local media reported.

A fire engine stands by the site of a fire in an alleyway, tangled in electrical wire and too narrow for vehicles to access, in New Delhi, India | Image: Manish Swarup/AP/Press Association Images

However, no details were immediately available on the cause of the fire.

India's Prime Minister Narendra Modi described the fire as "extremely horrific".

"My thoughts are with those who lost their loved ones. Wishing the injured a quick recovery," Mr Modi tweeted.

The fire in Delhi's Anaj Mandi on Rani Jhansi Road is extremely horrific. My thoughts are with those who lost their loved ones. Wishing the injured a quick recovery. Authorities are providing all possible assistance at the site of the tragedy.

— Narendra Modi (@narendramodi) December 8, 2019

Authorities are providing all possible assistance at the site of the tragedy, he said.

Fires are common in India, where building laws and safety norms are often flouted by builders and residents.

In 1997, a fire in a cinema in New Delhi killed 59 people.

In February this year, 17 people were killed by a fire in a six-storey hotel, also in the Indian capital that started in an unauthorised rooftop kitchen.