Firefighters with search dogs and buckets spent the night picking through what was left of a three-storey building in Brooklyn’s Flatbush neighbourhood, which gave way at around 4pm on Wednesday and slid into an excavation pit next door. By Thursday the death toll had climbed to at least eight. Seventeen or more were injured, including three firefighters, and four of the wounded were in critical condition.

Mayor Zohran Mamdani said he was “heartbroken” and asked people to keep clear of the Flatbush Avenue site, where about 250 fire and medical personnel were deployed. By chance an engine company was close by, so firefighters were digging people out almost immediately. Local television reported that a handful of people, one of them pregnant, were brought out alive that evening. The fire commissioner said the building’s residents included seven children, without saying whether any had died.

Nobody yet knows how many people may still be missing. Department chief John Esposito expects a full search of the debris to stretch over several days. The collapse also ripped a wall off the neighbouring property, exposing apartments and a stairwell to the street.

Investigators are focusing on the lot beside the 1930s structure, where crews were digging foundations for a new building. City inspectors had halted work there in the spring after the previous building was knocked down without proper protection for its neighbours. When demolition carried on regardless, the developer was fined $10,000, and the order was lifted in May. The buildings department has said the owners were seeking approval for a nine-storey project, larger than the three storeys already permitted.

Officials stress that it is too early to say whether the excavation caused the collapse, and the investigation is ongoing.