The exercise allows first responders to rehearse emergency response plans.
More than 900 firefighters on duty at 106 fire stations around Los Angeles conducted the drop drill, then drove around their districts to practice surveying for damage and assessing need for rescues, said department spokesman Brian Humphrey.
At Rosemont Avenue Elementary School, some students dove under desks while others did not and sprawled in their classroom with simulated injuries created with Hollywood-style makeup.
Firefighters searched the school, located and triaged the injured, laying them out on red, yellow and green mats depending on severity. Some students were tasked to show delayed onset of injuries after an evacuation.
The Great ShakeOut was first held in California in 2008 and participation has since spread around the globe. This year, Japan, Canada, Italy and Guam joined the drill. Thursday's drills were to conclude in Alaska and Hawaii at 10:17 a.m. local time.