SAN DIEGO - You can call it disaster training with a dose of the undead. San Diego hosted a zombie invasion on Halloween night and the creatures were invited.

Amid gunfire, zombies mobbed a Third World village. In the middle of the chaos was a top official with an aid organization surrounded by security details. Dozens of military, law enforcement, first responders and actors battled against a so-called "zombie apocalypse."

The drill was part of a 5-day counterterrorism summit organized by the HALO Corporation. The zombies were make-believe.

"Shooting zombies ... shooting blanks is good fun," said Jason Elder, a former sailor who played one of the security detail members.

The action was backed by Hollywood sets and special effects.

"I almost had to change my underwear… it was that intense," said Johnny Wing, an actor who took part in the scenario.

In the scenario, the aid official and his personal detail are trapped in a village overrun by zombies when a bomb explodes. The aid official maneuvers through the town. Some of his detail are bitten and must be taken to a medical facility for treatment.

Organizers chose the zombie theme because the unpredictability of zombies compares to real dangers, like an out of control enemy.

Also, the dreaded zombie bites can help train for a chemical warfare attack. Another parallel was the carnage of a zombie apocalypse compared to the panic of a world disaster.

"Because it's a mass casualty type event, it could induce mass hysteria, so what better way to show that," said Kit Lavell. His group, Strategic Operations, which is part of Stu Segal Productions, put on the scenario.

The scenario comes in the wake of two tongue-in-cheek zombie education campaigns, one by the Department of Homeland Security and another by the Centers for Disease Control and Prevention to increase awareness for emergency preparedness.