Kolkata: As the rush hour traffic moved over the arterial Diamond Harbour Road in south Kolkata on Tuesday, a section of the 50-year-old Majerhat bridge, that connects Behala to the rest of the state capital, collapsed, taking down cars, vehicles and buses along with it.

The major accident in the heart of Kolkata left citizens shocked as one person died and several others remained trapped under the debris for several hours before rescue workers could pull them out.

So far, official have confirmed 21 cases of injury. The injured persons have been taken to SSKM Medical College and Hospital and CMRI Hospital in the vicinity.

Fire brigade personnel engaged in the rescue work had earlier said 25 injured were pulled out from the rubble.

The Majerhat bridge in the crowded Alipore area caved in around 4.45 pm during rush hour. It runs over the Majerhat Railway Station. Apart from Behala, the collapsed bridge also connects vast areas of the south west suburbs and neighbouring South 24 Parganas district.

As the Sun went down and it started pouring, additional lighting arrangements were made to facilitate the rescue work at night.

One minibus, four cars and a few motorbikes which were hit by the collapse were seen lying at the accident site till evening.

An eyewitness claimed that some people in a minibus and private cars were trapped under the debris.

Chief Minister Mamata Banerjee, who is in Darjeeling for an official tour, said that rescue work was almost over and only a concrete slab remains to be cut to find out whether any person was trapped there.

Vehicles stuck on the section of Majerhat bridge that collapsed in Kolkata on Tuesday. (PTI Photo/Ashok Bhaumik)

She said there was a hut under the bridge where some labourers engaged in Metro rail construction work used to stay. "Had they been there during the time of accident, an unfortunate thing might have happened," she said.

Banerjee said that thousands of people pass through the area and the government has to probe the accident.

"A probe will be done by a committee headed by Chief Secretary Malay De to find out the cause of the collapse. Action will be taken against those whose negligence caused the accident. No one will be spared," she said.

She also announced a compensation of Rs five lakh to the family of the deceased and Rs 50,00 each to the injured.

Banerjee said she will visit the site on Wednesday, cutting short her North Bengal tour.

Prime Minister Narendra Modi termed the incident as "deeply unfortunate" and hoped for the speedy recovery of the injured.

Governor K N Tripathi, who visited the site, described it as "a big disaster".

"I have come to see the rescue work. It is a big disaster. I heard that maintenance of the bridge is entrusted with the PWD and the railways. The matter required to be enquired," he told reporters.

NDRF DG Sanjay Kumar said earthmovers are being used for clearing the area.

"We have to take into account the safety aspect while clearing the debris", he said.

NDRF personnel have engaged sniffer dogs to trace any person trapped under the debris.

The 450 metre-long bridge was built in early sixties and maintained by PWD, a member of mayor-in-council in the city municipal corporation said.

Some locals alleged the collapse might have been due to the construction of Metro railway pillars nearby but this was not immediately confirmed by the experts.

Rail Vikas Nigam Limited, which is executing construction of the Joka-BBD Bag metro corridor passing through the vicinity of Majherhat bridge, said there is "no relationship of Metro construction" with the incident.

The bridge connects Behala to other parts of Kolkata. (Image: News18)

Urban Development Minister Firhad Hakim said the government would undertake technical inquiry after the rescue work is over.

Asked whether the committee which look after the old bridges had given fit certificate to the Majerhat bridge, the minister said, "I cannot confirm it".

The bridge collapse hit Circular Railway services and local train services in Budge Budge-Sealdah line inconveniencing a large number of commuters, an Eastern Railway spokesman said here.

The local train services were suspended from 4.45 pm, he said. The train services in the Budge Budge-Sealdah section at around 9 pm, an ER spokesman said.

The bridge collapse hit traffic movement to and from vast areas in south-west Kolkata and adjacent South 24 Parganas district during the peak evening hours.

Trinamool leader Derek O'Brien tweeted, "Watching scenes of Majerhat bridge #Kolkata collapse. Devastating. Rescue teams, disaster management teams, Police CP, fire fighters already reach spot. Locals join. Rescue operations on. Prayers for those affected. Difficult to gauge enormity of tragedy as yet looking at visuals."

Opposition parties blamed the Trinamool Congress government and said its "callousness towards the repair of old bridges" was the main reason for the collapse.

"It is really unfortunate that the bridge has collapsed. The state government is solely responsible for it. The issue of repair of the old bridges is not at all in the agenda of TMC government," senior BJP leader Mukul Roy said.

State Congress president Adhir Chowdhury demanded an "answer" from Chief Minister Banerjee and Public Works Department Minister Hakim.

This is the third bridge collapse in the city in five and a half years.

An under construction flyover had collapsed in crowded Burrabazar area, the wholesale business hub of the city, on March 31, 2016 and had claimed 26 lives.

On March 4, 2013, a road bridge had collapsed in Ultadanga area in the northern part of the city but there was no casualty.