Three men engaged for demolishing an old two-storey building in central Calcutta were injured as a portion of the wall they were dismantling collapsed on them following a heavy shower on Tuesday morning.

There were reports of cave ins at two more locations in the city on Tuesday.

The scariest was reported at 7, Rajkumar Bose Lane in central Calcutta, near Wellington Square, on Tuesday afternoon.

Police identified the three injured persons as Sumit Singh, 42, Bimal Roy, 42, and Shahin Sheikh, 35. All three were labourers engaged for the demolition work who suffered from multiple injuries and have been admitted to Medical College Kolkata, the police said.

Portions of two more buildings collapsed in the Janbazar and Narkeldanga areas on Tuesday. There were no reports of anyone being injured or trapped, police said.

A portion of an old building collapsed on Rajendra Lal Street in Narkeldanga on Tuesday afternoon, while a portion of a wall on the first floor of a building on 24B, Rani Rashmoni Road, caved in on Tuesday morning.

Heavy rainfall only made dilapidated buildings across the city even more precarious.

Between 5.30pm on Monday and 5.30pm on Tuesday, the Met office recorded around 50mm of rain in Alipore.

The cyclonic circulation that was over north Bangladesh descended on Tuesday, triggering another sharp spell of rain in Calcutta in the afternoon. The city had already received more than one spell of rain between Monday night and Tuesday morning.

The intensity of the rain in most of south Bengal, including Calcutta, is expected to dip from Wednesday. North Bengal is likely to see heavy rain in the coming days, according to the forecast.

Around 2.50pm on Tuesday, the Maidan skyline looked ominously dark. The rain started minutes after. It was blinding in many parts for a good 20 minutes.

The booster pumping stations of the Kolkata Municipal Corporation recorded 85mm of rain in Jodhpur Park between 3am and 4pm on Tuesday. Ballygunge got 46mm and Belgachhia 47mm in the same period.

“The upper air cyclonic circulation over north Bangladesh and neighbourhood now lies over Gangetic Bengal and neighbourhood,” said a Met official.

“A trough now runs from the northeast Arabian Sea to south Bangladesh across Gujarat, Madhya Pradesh, Jharkhand and adjoining north Chhattisgarh and Gangetic West Bengal. The monsoon trough now passes through Rajasthan, Madhya Pradesh, Jharkhand and Digha in Bengal into the northeast Bay of Bengal,” he said.