New York Post is now breaking the story.
4-STORY FT. GREENE BUILDING COLLAPSES
By REUVEN FENTON and DAN MANGAN
A four-story building in the Fort Greene section of Brooklyn collapsed this afternoon, injuring at least three people and leading to the evacuation of adjoining buildings.
"It's completely destroyed," Alex Alamonte, 27, manager of the Associated Supermarket across the street from the Myrtle Avenue building, near the intersection of Ryerson Street.
Alamonte said the brick building began falling apart, for no apparent reason, at about 2 p.m.
"It fully collapsed from one second to another First a couple bricks fell down and then the whole front fell down Floor by floor it went down," said Alamonte. "It's a pile of rubble except the back left corner . . . the back wall is still standing."
"It was like Sept. 11. Out of nowhere the building just collapsed."
Police radio transmissions reported that at least three people had been injured in the collapse, and that officers were evacuating other nearby structures.
Here is a photo straight from Twitter by @irwin.
ETA: Another photo, slightly more up close, courtesy of @ryantomorrow...
ETA2: Google Street Map view of the original building, which must have been the "VESPER" building.