At least 64 people have been killed and 80 injured after a multi-storey building collapsed in the Indian capital, Delhi.

Investigators believe the five-storey building in a working class area of eastern Delhi had been weakened by recent flooding brought on by some of the strongest monsoon rains in decades.

The site of the structure lies next to the Yamuna river, which burst its banks in September and early October.

'There are many victims still trapped below the concrete rubble and iron rods. Our challenge is to evacuate them alive,' city police spokesman Rajan Bhagat said.

Throughout the night and early morning, rescuers and locals pulled out severely injured people and corpses.

Victims including children were carried away on stretchers to nearby ambulances.

The congested and narrow streets of the Lalita Park area of Laxmi Nagar made it difficult to bring in heavy lifting equipment, meaning rescue services relied on sledgehammers and a few hydraulic drills.

Witnesses said they heard shouts for help from under the debris.

Delhi Chief Minister Sheila Dikshit suggested the building might have been an unauthorised construction, and officials said an inquiry had been launched into the disaster.

The building is believed to have been mostly residential, but with some small businesses including a cloth exporting company and a food snacks group.

A sixth floor was being added, local people said, raising another possible cause of the collapse.

Enforcement of building regulations is lax in the Indian capital and minor accidents are common. The construction industry is also riddled with corruption, leading to the use of substandard materials.

The much-delayed and over-budget Delhi Commonwealth Games in October shone an unflattering light on many industry practices.

An investigation by India's leading anti-corruption body concluded that sub-standard concrete and anti-corrosion coatings for steel had been used in a host of public works, while safety certificates also appeared to have been faked.