At least one person is dead.
More than 150 firefighters are said to have battled the blaze, which is thought to have been caused by a gas explosion.
Squatters had occupied the high-rise, and firefighters fear more people may have been trapped inside.
Witnesses say flames spread quickly from one of the lower floors and set an adjacent building on fire.
Some 50 families had moved into the building after the Federal Police Force, which had been using it, vacated some years ago.
a nearby hotel was evacuated because of the fire.
The fire started at 01:20 local time and the flames spreading quickly.
The high-rise collapsed 90 minutes later.