A section of the overpass in the busy Bara Bazaar residential and shopping area in north Kolkata fell on vehicles and people moving underneath, trapping scores in their cars, trucks, and motorised rickshaws.
“We heard a loud rumble and then saw a lot of dust in the sky,” a witness told the New Delhi Television news channel, NDTV.
Mamta Banerjee, the top elected official of West Bengal state, said 21 people had been confirmed dead. Banerjee visited the collapse site and said a private builder had missed several deadlines for completing the overpass.
Army troops and personnel from the National Disaster Response Force joined efforts to extract people from vehicles that lay under massive concrete blocks and metal debris. Huge cranes and other rescue equipment reached the site and began clearing the rubble. Workers also used gas cutters to pry open the slabs.
OP Singh, the chief of the disaster response force, said the operation was a “very, very challenging task”.
Rescuers were using sniffer dogs and victim locating cameras to find trapped people, Singh told reporters.
More than 70 injured people were admitted to two hospitals in Kolkata, the state capital, hospital officials said.
Television images showed the bloody legs of some of trapped people jutting out of the collapsed girders and concrete slabs.
The contract to construct the overpass was signed in 2007 and it was expected to be completed within two years. Banerjee accused the previous Communist government in West Bengal of not adhering to building regulations.
“We completed nearly 70% of the construction work without mishap,” said KP Rao, a top official with the IVRCL Infrastructure firm.