At least 12 people, including eight children, were killed and seven injured when two floors of an illegally constructed three-storey residential building collapsed on an adjoining single-storey house in suburban Mumbai, officials said on Thursday.

The incident took place around 11.15pm on Wednesday, when Mumbai experienced heavy rain through the day, at the New Collector Compound on Abdul Hamid Road in the Malwani area of suburban Malad, the officials said.

The three-storey building had been constructed illegally and had suffered damage in Cyclone Tauktae, which passed close to the Mumbai coast last month, police said, adding that its contractor had been arrested on the charge of culpable homicide.

The Maharashtra government announced an ex gratia of Rs 5 lakh each for the kin of those who lost their lives in the house collapse, while the Centre will give an additional Rs 2 lakh.

The second and third floors of the three-storey building collapsed on the adjoining single-storey house, said Santosh Dhonde, acting ward officer of the city’s P-North ward. Fire brigade and other agencies immediately rushed to the spot and started a search-and-rescue operation, the official from the Brihanmumbai Municipal Corporation (BMC) said.

Eight children and four adults died, he said, adding that most of the deceased were from two families. Seven others were injured and the condition of one of them was critical, he said. People rescued from under the debris were taken to nearby hospitals, he added.

The deceased have been identified as Sahil Sarfaraz Sayyed, 9, Arifa Sheikh, 9, Shafiq Md Saleem Siddiqui, 45, Tausif Shafiq Siddiqui, 15, Aalisha Shafiq Siddiqui, 10, Alfisa Shafiq Siddiqui, 1, Afina Shafik Siddiqui, 6, Ishrat Bano Shafiq Siddiqui, 40, Rahisa Bano Rafik Siddiqui, 40, Tahes Safik Siddiqui, 12, and John Irranna, 13, and a 60-year-old man named only as Sardar.

According to civic and fire brigade officials, some people might still be trapped under the rubble and the search-and-rescue operations were on. According to the BMC, the collapsed building was located on collector’s land and its owner got permission from the collector’s office while constructing a permanent structure.

However, joint commissioner of police (law and order) Vishwas Nangre Patil told reporters that the building had been constructed illegally and had serious structural faults. During Cyclone Tauktae last month, the building suffered damage, he said, adding Wednesday’s incident could have been averted if proper precautions had been taken.

An FIR under IPC Sections 304 (2) (culpable homicide not amounting to murder), 336 (act endangering life or personal safety of others), 337 (causing hurt by act endangering life or personal safety of others), 338 (causing grievous hurt by act endangering life or personal safety of others) and 34 (common intention) has been registered against the building contractor, Ramzan Nabi Shaikh, its owner Rafique Siddiqui (who lost nine members of his family) and others, the police said.

Contractor Ramzan, 34, a resident of Malwani, was picked up by police after the incident for questioning and later placed under arrest, said Dilip Sawant, additional commissioner of police (north region).

Prime Minister Narendra Modi expressed grief at the loss of lives in the building collapse and announced Rs 2 lakh ex gratia each for the next of kin of the deceased from the Prime Minister’s National Relief Fund.

In a condolence message from the Prime Minister, his office tweeted: “Pained by the loss of lives due to the collapse of a structure in Malad West, Mumbai. In this hour of grief, my thoughts are with the bereaved families. I pray that the injured recover at the earliest.”

A sum of Rs 50,000 will be provided to each of the injured, Modi said.

The Maharashtra government separately announced an ex gratia of Rs 5 lakh each to the kin of those who lost their lives in the tragedy. It also said that the medical expenses of the injured would be borne by the government.

Chief minister Uddhav Thackeray condoled the loss of lives and visited Shatabdi Hospital in the city on Thursday to enquire about the well-being of the survivors.