At least five people, including two women, were killed and several others injured after an under-construction five-storey building collapsed in the Garden Reach area of Kolkata, police said on Monday.

The toll could go up since at least four people were spotted trapped under the debris and only one of them showed signs of life, a fire services official, engaged in rescue operations, said.

Kolkata Mayor Firhad Hakim said the rescue operations were carried out on war footing at the site where the building was being constructed illegally.

While Md Wasim, the promoter of the building, was arrested, the mayor said stringent action would be taken as per law.

West Bengal Chief Minister Mamata Banerjee visited the building collapse site at Azan Molla Lane in the city's western periphery and assured locals of stern action against illegal construction.

In a horrific accident, the under-construction five-storey building collapsed around midnight, Hakim said.

“We are using gas cutters and other equipment to clear the debris and reach those who are stuck underneath. It's taking a long time since we are proceeding cautiously towards the victims,” the fire services official told PTI, adding that the personnel from NDRF, the state and Kolkata Police disaster management teams were also working in tandem.

Owing to the massive pile-up of debris, rescue workers are finding it tough to reach those who have been trapped, he said.

"We have compiled a list of victims of the building collapse. Five people died and two of them were women. Of the 15 injured people, 11 are undergoing treatment at hospitals and four were discharged after preliminary treatment," a senior officer said.

"Sad to learn about the house collapse disaster of an under-construction building in the Garden Reach area of the Kolkata Municipal Corporation. Our Mayor, Fire Minister, Secretaries and Commissioner of Police, civic, police, fire and disaster management officers and teams (including NDRF, KMC and KP teams) have been on site throughout the night for mitigating the disaster," the chief minister wrote on X.

She said the government will provide compensation to the next of kin of each deceased and the injured persons.

"We stand by the distressed families and rescue operations shall continue," Banerjee said on the microblogging site.

Hakim, also West Bengal's urban development minister, said, "I spoke to the chief minister and we will provide Rs 5 lakh to the next of kin of each deceased and Rs one lakh to each injured person."

TMC national general secretary Abhishek Banerjee said the building collapse incident is "extremely sad" and asserted that it should not be politicised.

"The opposition leaders, who are raising various questions in this regard, for them, I would say that politics can wait. We can do politics later, but at the moment we should focus on rescuing the people who are stuck. We hope that such incidents are not repeated. All institutions should work in tandem," he said.

The chief minister hoped that those trapped under the debris would be rescued soon.

"This is an illegal construction. I express my condolences to the family. I will urge the administration to take strict action against those involved in the illegal construction," she said after visiting the injured in a hospital.

This is Banerjee's first public appearance after she fell at her home and suffered injuries on Thursday evening. She also underwent stitches.

Banerjee with her bandaged forehead visited the building collapse site this morning.

She said the authorities should have been more vigilant when the illegal construction was going on.

Admitting that illegal constructions in the area were rampant, Hakim said, "It has been a trend here and also in some other areas since the Left Front era."

He also admitted that there could have been a "lapse on the part of the officials" for failing to monitor whether constructions in the locality were being made in accordance with law.

Hakim said, "It is not the job of the local councillor but of the civic body officials to inspect whether constructions are taking place according to sanctioned plans from Kolkata Municipal Corporation or not."

The chief minister, meanwhile, expressed her distress over the incident and urged the administration to take necessary action against those involved in the illegal construction.

"The government stands by the affected families," she said.

State Fire and Emergency Services Minister Sujit Bose said the rescue operations are underway on a war footing and those trapped under the debris would be brought out soon.

Kolkata Police Commissioner Vineet Goyal visited the spot and took stock of the rescue operations.

According to locals, who were the first responders, concrete chunks fell from the building before it collapsed.

There was a loud sound and a thick cloud of dust engulfed the area as soon as the building collapsed. The debris fell on nearby shanties in the densely populated area, they said.

"Although no one lived in the under-construction building, it collapsed on the adjacent shanties. We fear that many individuals might still be trapped under the rubble," said a resident.

In a post on X last night, Leader of Opposition in the West Bengal Assembly Suvendu Adhikari said, "I urge @chief_west, Secretary @HomeBengal, @CPKolkata to immediately involve West Bengal State Disaster Management Team for immediate Rescue & Relief." "I am receiving frantic calls regarding probable casualties. Please dispatch any team which can help in rescuing the victims, be it fire Servicemen, police or any other team," he said.

Adhikari also shared pictures from the building collapse site.