I picked this classic up in Spain whilst on my holidays. Good luck finding a copy outside of Spain. The movie is taken from the point of view of a cameraman named Pablo and a reportor called Angela. Nearly all of the movie is spent in a five storey building where an infection has been quarantined.

Spoiler Alert From Now On!
The Zombies: The zombies in this film are nearly impossible to kill. They can be temporarily stalled by bullets or blunt trauma as seen. An unspecified enzyme rebuilds what is needed to survive.

I'll finish this off later.