It happened just after 4 p.m. at a vacant two-story residential building on Logan Street in East New York.
No injuries were reported, but an adjacent building was evacuated as a precaution, affecting 21 tenants.
The FDNY and Department of Buildings responded to the incident.
DOB inspectors are conducting an inspection of the structural stability.
The department said a full vacate order was issued in April 2018 after the building was found to be uninhabitable.
An emergency declaration was issued last December for full demolition of the structure after an inspection found it had begun to lean.
Permits and contractors for the demolition were in the process of being secured when the collapse occurred. The remaining structure will be demolished.
Displacec residents were escorted into their homes to get clothes for the next few days. They were offered relocation assistance by the American Red Cross.
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