Emergency teams staged a mock operation Thursday to respond to a catastrophic 7.8-magnitude quake in Los Angeles, saying the West Coast megalopolis needs to be ready for an "overdue" Big One.

Some 300 people took part in the office-based drill organized by LA County's Office of Emergency Management, based in a center especially built to withstand a major earthquake, and serve as a hub to coordinate disaster services.

Los Angeles sits on the so-called "Ring of Fire," which circles the Pacific and has produced a number of devastating earthquakes, including Japan's March 2011 quake and tsunami that killed thousands of people.

But a Big One is overdue in California.

"It is not meant to scare people, but they need to prepare for this," said Margaret Vinci, head of the Office of Earthquake Programs.

"We have not experienced a magnitude 7.8 earthquake since 1857... So we are overdue and people need to understand what is gonna be like, our life is gonna change.

"But the more you're prepared, the more you're going to be able to recover faster and survive," she added.

Angelenos are used to thinking about quakes, as schools and office buildings hold regular drills. Many people have emergency kits at home and at work, or in their car in case the worst happens.

Water is among the most crucial supplies. Authorities recommend that people have enough water stored for at least one gallon (3.8 liters) per person to last at least 7-10 days. "Emergency services are not gonna be there for a while," said Vinci.

"A lot of our water pipes are going to break, they are about 100 years old. Gas pipes will be broken. Communications will be down, our cell phones will be unusable. Electricity will be down.

"And this would be for days, weeks, if not months," she added.

Only last week, LA was hit with a relatively modest, 4.7-magnitude quake, the strongest to hit the area since 2010. The quake shook buildings in Los Angeles even though its epicenter was some 100 miles (160 kilometers) southeast of the city.

The Emergency Operations Center is not built on the ground.

"It's built on base isolators. That means that a 7.8 earthquake shakes the building... but you will be like on a boat," spokesman Ken Kondo told reporters.