The fire broke out in the attic, with video posted online showing large flames licking around the top of the building.
Fire crews were called to Westbourne Street just before 2.30am.
The property was made up of four flats and all the people inside had made their way out.
There were no injuries to anybody.
Two fire engines from Hunslet, one from Leeds, along with the aerial ladder platform, were called to the scene.
Four firefighters used two pumps and a fan to extinguish the fire.
Smoke detectors were fitted inside but they did not go off.
A specialist fire investigation officer is on scene to try to find out what caused the fire.
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