Indian police on Friday opened a case of culpable homicide against the company building an overpass that collapsed in the eastern city of Kolkata, killing at least 23 people and injuring dozens more.

Rescuers worked all night with cranes and jackhammers to clear concrete slabs and steel girders from the 100-meter (110-yard) length of the overpass that broke off suddenly and crashed down on pedestrians and vehicles on the road below.

Ninety were rescued, many with serious trauma injuries, but chances of finding survivors in the wreckage had dwindled nearly a full day after Thursday's disaster in a teeming commercial district near the city's Girish Park.

"It is being ensured that there are no more dead bodies under the debris," S.S. Guleria, a deputy inspector general of the National Disaster Response Force, told Reuters Television.

Television channels broadcast images of a street scene with two autorickshaws and a crowd of people suddenly obliterated by a mass of falling concrete that narrowly missed cars crawling in a traffic jam.

Chief Minister Mamata Banerjee, whose center-left party is seeking re-election next month in the state of West Bengal, said those responsible would not be spared and blamed the previous state government that had awarded the overpass contract in 2007.

Yet she herself faces questions about a construction project that has been plagued by delays and safety fears under her rule.

A newspaper reported last November that Banerjee wanted the overpass - already five years overdue - to be completed by February. Project engineers expressed concerns over whether this would be possible, the Telegraph newspaper said at the time.

The disaster could play a role in the election in West Bengal, whose capital is Kolkata. The poll is one of five being held this month that will give an interim verdict on Prime Minister Narendra Modi's nearly two years in power.

Indian company IVRCL (IVRC.NS) was building the 2-km (1.2-mile) Vivekananda Road overpass, according to its web site. Its shares fell another 6 percent on Friday as police announced they had opened a case of culpable homicide.

The local offices of IVRCL were sealed and a police team was on its way to interview bosses at the company's headquarters in the southern city of Hyderabad, according to reports.

A senior IVRCL manager had drawn national condemnation for calling the disaster an act of God.

"We did not use any inferior quality material and we will cooperate with the investigators," the company's director of operations, A.G.K. Murthy told reporters on Thursday. "We are in a state of shock."

Years of delays may have caused corrosion to metal elements of the overpass, undermining its stability, according to rescuers who examined the wreckage. Locals said that concrete was poured on the stretch the night before its collapse.

OVERNIGHT EFFORT

Rescue operations were slow initially, with local residents forming crowds several deep as they tried to help trapped people.

But three cranes working overnight managed to clear some of the wreckage and free access to vehicles with people believed to be still trapped inside.

Harrowing news images showed the leg and arm of one dead man protruding from under a massive steel girder. The broken leg of an unconscious man flapped uselessly as rescuers gripped his other three limbs to carry him away.

Getting survivors to hospital was complicated by a lack of access for ambulances to the overpass, hemmed in by buildings on either side. Safety standards were lax, witnesses said.

"Every night, hundreds of laborers would build the flyover and they would cook and sleep near the site by day," said Ravindra Kumar Gupta, a grocer who pulled out six bodies, together with his friends.

"The government wanted to complete the flyover before the elections and the laborers were working on a tight deadline. Maybe the hasty construction led to the collapse."