(AFP) - Emergency workers battled through the night into Friday to reach dozens of people still believed trapped under a flyover that collapsed in India, killing at least 22 others.

Specialist rescue teams were using heavy cutting machinery and drills to reach an unknown number of people buried under the 100-metre (330-feet) section of road in Kolkata.

Gruesome pictures showed limbs and bloodied bodies sticking out from underneath huge slabs that had come crashing down on pedestrians, cars and other vehicles.

"Four hundred men from NDRF (the National Disaster Response Force) and 300 Indian army men along with hundreds of police and local officials are at the spot," spokesman Anurag Gupta told AFP on Thursday evening.

Authorities had sealed off the accident site to members of the public, who in the initial hours were seen trying to pull away concrete slabs with their bare hands.

Workers struggled to get cranes and other large machinery through the narrow streets of Burrabazar, one of the oldest and most congested parts of the city, where locals desperately waited for news of missing loved ones.

"Everything is finished," screamed Parbati Mondal, whose fruit-seller husband had not been seen since the accident.

An injured builder told AFP at the scene that he had been working on the structure before it collapsed and had seen bolts come out of the metal girders.

"We were cementing two iron girders for the pillars, but the girders couldn't take the weight of the cement," said 30-year-old Milan Sheikh before being taken away to hospital.

"The bolts started coming out this morning and then the flyover came crashing down."

Many locals said they were fleeing their houses for fear that more of the damaged structure could collapse.

"We heard a massive bang sound and our house shook violently. We thought it was an earthquake," 45-year-old resident Sunita Agarwal told AFP.

"We're leaving -- who knows what will happen next."

Speaking late Thursday, Javed Ahmed Khan, disaster management minister for the state of West Bengal put the death toll at 22.

Other officials said 92 people had been rescued, some of whom were in a critical condition in hospital.

Construction on the two-kilometre-long flyover began in 2009 and was supposed to be completed within 18 months but has suffered a series of hold-ups.

K.P. Rao, a representative of the Indian construction company IVRCL, which was contracted to build the giant flyover, called the disaster an "act of God".

Their offices in Kolkata were sealed by investigators and police filed an initial charge of "culpable homicide not amounting to murder" against the company.

The disaster is the latest in a string of deadly construction accidents in India, where enforcement of safety rules is weak and substandard materials are often used.

The tragedy came just days before the World T20 cricket final, which is set to draw thousands of fans to the city this Sunday.

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