Rescuers work at the site of a building that collapsed in Mumbai. Picture: Rafiq Maqbool/AP

Mumbai - Rescue workers in Mumbai searched for more than a dozen people feared trapped in a 117-year-old, six-storey building that collapsed early on Thursday, following two days of torrential rain in India's commercial and financial hub.

Eleven people had been confirmed dead, and 14 had been injured and taken to hospital, with four firemen also injured, the chief fire official said.

"There was a massive bang. We couldn't see anything due to the dust and smoke. Once the dust settled, we realised it was a building collapse," said area resident Amina Sheikh.

Disaster struck early in the morning as Mumbai was emerging from two days of heavy rain that flooded the city and killed 14 people.

The collapse was the second in Mumbai in a little over a month. In late July, 17 people were killed when a four-storey building crumbled after undergoing suspected unauthorised renovations.

The building that collapsed on Thursday, in one of the most densely populated areas of the city, had been declared dilapidated by the city's municipal housing authority in 2011.

But it was still inhabited by an unknown number of residents.

Desperate relatives of those trapped pleaded with rescuers to help find their loved ones after getting phone calls from trapped survivors. About 200 police and fire personnel sorted through the debris.

Police had yet to determine what caused the collapse near Crawford market, a landmark of south Mumbai's old city with narrow streets packed with markets and shops. Many Muslims live in the neighbourhood.

Rescuers, including a team from the National Disaster Response Force, said the area's narrow roads were making it difficult to bring in the excavators.

The building housed a sweet shop warehouse on the ground floor. Smoke rose from the ruins.

A housing trust that was looking to redevelop the area said the building had been declared unsafe in 2011 and the housing board had offered alternative accommodation to tenants, but only seven families had moved out by early 2014.

One residents in the area said people had not been given proper details of what type of new housing they would be provided, making them reluctant to leave.

It was not immediately clear what housing regulators had done to encourage residents to evacuate.

The building was also among 791 buildings that the city's municipal corporation has listed as dangerous this year.

Only a few of those buildings have been evacuated or demolished, and more than 500 of them were still being occupied, an official of the Brihanmumbai Municipal Corp told Reuters.