NEW DELHI (AFP) - At least 64 people were killed when a multi-storey building in a crowded area of New Delhi collapsed, with the death toll set to rise Tuesday as rescuers made slow progress amid the rubble. Investigators believe the five-storey building in a working class area of eastern Delhi, which caved in late Monday, had been weakened by recent flooding brought on by some of the strongest monsoon rains in decades. The site of the structure, now a crumpled heap of concrete resembling the aftermath of an earthquake, 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 told AFP. We can confirm that 64 people are dead, he added, saying 80 were being treated in hospitals. Throughout the night and early morning, rescuers and locals pulled out severely injured people and corpses, with victims including several children who 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. The building fell like a pack of cards. I saw people high up hanging onto remaining bits of the walls. Some were trying to jump out but they couldnt, others were trapped, Gurwinder Singh, a local taxi driver, told AFP. Girija Devi, a mother of four who worked at a tailors workshop in the building, said: I was pulled out last night by some of the neighbours but my sister is still stuck below 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. I think it is the carelessness of the builder who did not build a strong enough building to withstand a flood that came about a month ago, she told the NDTV news channel. M.P. Singh in the Delhi police control room told AFP that the owner of the building, a local businessman who owns a cement factory, had been arrested and charged with culpable homicide not amounting to murder. 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 Indias 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. The enquiry that we will set up tomorrow will bring out the truth and will hopefully identify those that are guilty either individually or collectively, Dikshit said Monday.