Rescue efforts were still on and would continue through the night.
Banerjee, who rushed to Kolkata after cancelling election rallies in West Midnapore district, had earlier confirmed 18 fatalities and said 17 people were still in hospital after sustaining injuries in the ghastly disaster which occurred around 12.30 p.m.
A National Disaster Response Force (NDRF) official put the number of injured around 100. "Eighteen people died and over 70 were rescued. Seventeen of them are still in hospital," the chief minister had said earlier.
Hundreds of locals were the first to reach the site at Posta area in the city's northern part to see how best they could rescue those buried in the heaps of debris before official rescue workers and police joined them.
Nearly 500 army men that included 10 military medical teams, ambulances, paramedics, rescue teams with sophisticated gas cutters and cranes, besides police, disaster response teams and fire brigade personnel transported the badly injured as well as nearly dying to hospitals an extricated corpses. The soldiers are using specialized equipment to rescue those trapped under tonnes of steel and concrete, a defence ministry spokesman said. Prime Minister Narendra Modi expressed "shock" over the tragedy. "My thoughts are with the families of those who lost their lives," he tweeted. "May the injured recover at the earliest."
Home Minister Rajnath Singh said he had spoken to NDRF Director General O.P. Singh to coordinate relief work. The accident spot represented a horrific site. Body parts were strewn in the debris. Blood was splattered on the streets.
A video of the disaster showed the Vivekananda Road Flyover -- whose foundation was laid in 2008 and where work began in February 2009 -- suddenly crashing with a roar, giving no time for anyone under it to escape.
"There was a sudden thundering noise" as the flyover crashed, a witness said.
He said he saw the flyover collapse over taxis, auto-rickshaws and other vehicles besides people who were walking under it.
A witness claimed a mini bus was caught in the disaster, but late in the evening, police said the vehicle was not there under the debris. With the collapsed flyover covering the entire road, rescue operations were badly hampered as cranes found it difficult to reach the spot. Later, people formed human chains to regulate the flow of soldiers. Amid sights of despair and distress, angry locals vented their ire against the state government's "feeble" attempts to rescue the injured, alleging that the state's disaster management units "arrived late" and came virtually "empty-handed". Many people protested when city mayor Sovan Chattopadhyay arrived at the spot to take stock of the situation. The chief minister, who personally supervised the rescue efforts, announced a compensation of Rs.5 lakh to the families of the dead, Rs.2 lakh each for the critically injured and Rs.1 lakh for those who suffered minor injuries.
Banerjee formed two expert teams to look into the reasons for the mishap and suggest remedies.
Following her instructions, police filed an FIR against the implementing agency IVRCL Infrastructure, whose owner described the disaster as an "act of god". Experts from Kharagpur-IIT and Jadavpur University, however, told IANS that lack of proper planning, delays, lacunae in design and bad tendering could have triggered the collapse.
The long-delayed 2.5-km flyover was expected to tackle congestion in Burra Bazar area -- the location of one of the largest wholesale markets in Asia -- up to the Howrah station, the gateway to the city. It was scheduled to be ready in 2012 but land acquisition issues delayed its completion. The implementing agency, too ran into financial troubles. While Governor K.N. Tripathi sought a report from the Mamata Banerjee government, the incident led to a political slugfest between the ruling Trinamool Congress and the opposition in the poll-bound state. State Congress chief Adhir Ranjan Chowdhury demanded arrest of state urban development minister Firhad Hakim and the city mayor and announced he would file a public interest litigation seeking a probe. While Banerjee tried to put the blame on the Left Front pointing out that the contract was given and work started during its rule, CPI-M leader and former urban development minister Asok Bhattacharya held Hakim responsible. Describing the incident as example of the "corrupt ways of the Trinamool", the Bharatiya Janata Party demanded a probe, preferably by the CBI.