Using saws, small cranes and their bare hands, rescuers searched for survivors under the crumbled concrete and twisted steel left when an overpass collapsed in Kolkata, killing at least 23 people.
With more than half the debris cleared by Friday morning, some 67 people have been pulled out alive, Kolkata police Sgt P Chakraborty said.
But more people were still feared trapped. It was not clear how many people were missing, while more than 80 were injured.
Smashed yellow taxis, a crushed truck, destroyed rickshaws and the legs of trapped people jutted from the fallen girders and concrete.
The overpass spanned nearly the width of the street and was designed to ease traffic through the densely crowded Bara Bazaar area of the capital of the east Indian state of West Bengal.
About 300ft of the overpass fell, while other sections remained standing.
"I heard an explosion, a solid one," said resident Rabindra Kumar Gupta, who had been home eating lunch when the overpass crashed down without warning around 12.30pm local time on Thursday.
"My apartment shook. The whole building shook. When I looked outside, there was a lot of smoke."
Crowds waited anxiously near the rescue area to see if neighbours and friends had survived. The area is a place where street vendors and service workers regularly plied their trades
"There used to be a tailor who sat here on this corner. We wonder about him. A cigarettes and tobacco vendor - we knew everyone who used to stay around this crossing," resident Pankaj Jhunjhunwala said.
"Until this rubbish is removed, we can't say for sure where they are or how this happened."
Police said 39 of the more than 80 people rushed to hospital were still being treated on Friday morning.
With army troops and personnel from the National Disaster Response Force joining the effort, police said they expected the rescue and clean-up to be completed by the end of the day.
Huge cranes and other equipment were brought to the site to begin clearing the rubble. Workers also used cutting torches to break up the slabs.
The operation was a "very, very challenging task" said OP Singh, chief of the disaster response force. Rescuers also used dogs and special cameras to find people who were trapped, he said.
Prime Minister Narendra Modi, who was in Washington at the time of the collapse, said he was "shocked and saddened" by the collapse.
"My thoughts are with the families of those who lost their lives in Kolkata. May the injured recover at the earliest."
Chief Minister Mamata Banerjee, the senior elected official of West Bengal state, who has been campaigning for re-election this month, told reporters that a private builder had missed several deadlines for completing the construction.
The contract for the overpass was signed in 2007 and it was expected to be completed in two years. Mr Banerjee accused the previous Communist government in West Bengal of not adhering to building regulations.
"We completed nearly 70% of the construction work without any mishap," said KP Rao, an official of IVRCL Infrastructure company, which was building the overpass.
"We have to go into the details to find out whether the collapse was due to any technical or quality issue."
Building collapses are common in India, where regulations are poorly enforced and construction companies often use substandard materials.