Horrifying footage showed people shouting for help as flames and smoke billowed around them.
Seven people including three firefighters and a minor have been hospitalised.
The raging inferno is understood to have started after 5.30pm local time on Thursday, inside a building located at a roundabout between Maestro Rodrigo and General Avilés avenues in Valencia, Spain.
A tenant told local media that the fire stared in one of the units and spread throughout the building.
Video filmed from the ground showed residents standing helpless on their balconies as fire raged on the floors above and below them.
The top of the building appeared to be crumbling as bright orange flames engulfed dozens of residences.
In one clip, an emergency responder standing at the top of a tower crane looked to be reaching for someone who was trapped.
Valencia's Emergency Coordination Centre reported several people had suffered injuries as at 7.49pm local time, including firefighters and members of the public.
The organisation wrote on X: "A firefighter with a wrist fracture has been transferred in a BLS unit to the General Hospital.