It happened at about 3:40 p.m. in a four-story building at the corner of East 13th Street and Third Avenue. Firefighters got the fire under control about 50 minutes later.
There is a store on the ground level of the building and apartments on the three floors above it.
The fire was in the machinery room on the roof. It's not clear what damage was done to the penthouse. The unit had just sold for $4.4 million.
Here's video from Eyewitness News viewer Connor Scalleat:
Fire on 13th & 3rd. NYFD handling it. Hope no one is hurt. pic.twitter.com/MMblm6oU40— Connor Scalleat (@connorscalleat) August 27, 2015
No people in the building were hurt in the fire, but two firefighters suffered minor injuries.
Here are the road closures as a result of the fire: Third Avenue between East 14th and East 12th streets, as well as East 13th Street between Second and Third avenues.
Stay with abc7NY for the latest on this developing story.