Seven firefighters were hospitalized in a rare seven-alarm fire Monday evening at a Far North Dallas apartment complex that is under construction.

The blaze, caused by an electrical short, continued to burn this morning, Dallas Fire-Rescue spokesman Jason Evans said. At its peak, 140 firefighters responded to the scene.

Three of the firefighters were injured when a floor collapsed, Evans said. The cause of the other injuries was undisclosed. All had been treated and released by this morning.

The fire began about 5:45 p.m. Monday in electrical meters outside the unoccupied Gramercy on the Park Apartments, at the southeast corner of the Dallas North Tollway and George Bush Turnpike.

Evans said the blaze was hidden in the building's walls and floor space, making it hard to determine whether it had been extinguished.

Because of that uncertainty, firefighters left the building for their own safety and the fire was elevated to seven alarms.