Thirty-five families were evacuated from two buildings in Shibtala Lane, Tijala, on Wednesday evening after one of them — a five-storey apartment block — tilted towards the other.

Civic engineers and residents of the two buildings said the apartment block had started tilting several days ago.

Police and the civic body ordered evacuation after local residents raised the alarm as the gap between the two buildings closed.

An engineer of the Calcutta Municipal Corporation (CMC) said the gap between the terraces of the two buildings had reduced to 2ft, while the gap at the ground-floor level is 6ft.

The tilt could be the result of stress on the building’s foundation, the engineer said. No cracks were, however, visible on the building’s exterior. “The reason for the tilt can be confirmed after a detailed analysis,” the engineer said.

“The building at 12/11 Tiljala Shibtala Lane was built about eight years ago. The foundation of the structure may have come under stress during subsequent construction around the building. Local residents said the adjacent building was erected only four years ago,” he said.

Civic engineers will also check municipal records to find out whether the building had a sanctioned plan.

The residents were evacuated around 9pm on Wednesday. Ahmedi Begum, who lives on the second floor of the building that has tilted, said the police asked them to leave. “We were in our house. There was no vibration and we didn’t feel anything, but the police asked us to vacate the house,” she said.

Mohammad Azad, who lives on the first floor of the building, said the building had started leaning about two months ago. “No one said anything all these days. Suddenly there was panic on Wednesday. Residents of the adjacent building felt the building would collapse,” he said.

“An inspection of the building on Thursday morning confirmed that it had tilted over a period of time. It is tough to say whether it started tilting a few days ago or a couple of months ago. But it surely did not tilt in a day,” an engineer said.

A team of policemen was posted outside the buildings on Thursday to ensure that none of the residents returned to their flats. They were, however, allowed to go in and collect their belongings.

“We didn’t get much time to bring out our stuff on Wednesday. I went back and took some clothes for my children on Thursday,” said Ishrat Parveen, who lives in the other building. There were about 25 families living in the building that tilted, while the adjacent building had about 19 families.