A three-storey under-construction warehouse collapsed in the Taratala area of west Kolkata on Wednesday afternoon, trapping several people under the debris and triggering a large-scale rescue operation.

A Kolkata Police official said at least 10 people had been rescued and shifted to a nearby hospital.

“The roof of the warehouse located on Transport Depot Road near Brace Bridge in the Taratala area collapsed around noon. Our officers have reached the spot. Some people were working at the site at the time of the incident. We fear that quite a few people may be trapped under the debris,” the official said.

According to eyewitnesses, massive iron beams and concrete slabs came crashing down while construction work was underway.

“Construction activities were taking place on the ground floor while the RCC structure for the first and second floors had been completed. The entire structure has come crashing down,” an eyewitness said.

Several people at the site said they could hear trapped workers crying for help from beneath the rubble.

A fire department official said the collapse occurred during casting work on the structure. He also alleged that substandard materials may have been used in the construction of the warehouse.

Personnel from Kolkata Police, the Disaster Management Group, Civil Defence and Fire and Emergency Services launched rescue operations immediately after the incident.

Army personnel also joined the operation, while cranes and heavy lifting equipment were deployed to remove twisted iron beams and concrete debris.

Rescue teams used gas cutters to cut through the wreckage and began vertical drilling at multiple points in an effort to reach those trapped underneath.

“We are following the cries for help coming from under the debris. At the same time, we are assuring the trapped people that they will be rescued soon,” a member of the Kolkata Police Disaster Management Group said.

The state government activated Disaster Management Group control rooms and issued helpline numbers for information related to the incident.

Control room numbers 1070, 8697981070 and 033-22143526/22535185 were made operational at the state secretariat.

Some local residents alleged that illegal construction activities had been taking place in the area for a considerable period.

State minister Indranil Khan, who reached the site, said the immediate focus was on rescue efforts.

“We will definitely look into the causes of the accident and whether there were any irregularities. But right now, the priority is to rescue as many victims as possible,” he said.

Urban Development Minister Agnimitra Paul and Kolkata Municipal Commissioner Smita Pandey also visited the site to monitor the rescue operation.

Rescue efforts were continuing at the time of filing this report.