Flames broke out shortly before 11:00 a.m. on 9th Street between 2nd and 3rd Avenue in the Gowanus section.
Officials said the fire started on the 2nd floor and spread to the third. The residents of several apartments escaped on their own without injury.
The flames spread to a second building before the 140 responding firefighters got things under control.
Two of those firefighters suffered minor injuries to their knees, officials said.
The cause of the fire is under investigation.
The building where the fire started is more than 100 years old and a wooden structure, which may have helped to fuel the flames, the FDNY said.
11 adults who live in ten residential units in the buildings were relocated by the ARC to area hotels.
MORE NEWS: Nearly 200 residents displaced after torch ignites massive fire in Queens
Illegal use of torch caused massive Queens fire: FDNY
----------
* More Brooklyn news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube
Submit a tip or story idea to Eyewitness News
Have a breaking news tip or an idea for a story we should cover? Send it to Eyewitness News using the form below. If attaching a video or photo, terms of use apply.