That's actually part of a whole chapter in World War Z. A mercenary from the rich people's resort who later ditched them reveals that once the common people started showing up to their door rather than zombies, an immediate fight broke out between all of the residents and their staff, with most of them killing each other. The mercenaries refused to intervene because they were hired to kill infected, not normal people, and had no loyalty to the rich residents.

The whole thing was broadcast live because the owner of the resort wanted to flaunt their status during the great panic.