California on Thursday launched the country's first earthquake warning system in the hope that residents will be alerted within seconds of a possible impending disaster and can "drop, cover and hold on."

The app, created by the University of California, Berkeley, and unveiled on the 30th anniversary of the deadly Loma Prieta quake, uses ground motion sensors located across the state to detect the start of earthquakes before humans can feel them.

"Nothing can replace families having a plan for earthquakes and other emergencies," Governor Gavin Newsom said in unveiling the warning system.

"And we know the Big One might be around the corner. I encourage every Californian to download this app and ensure your family is earthquake ready."

The cellphone app called MyShake can provide potentially life-saving seconds of warning before the ground starts to shake from a nearby quake -- enough time to drop, cover and hold on to help prevent injury, Newsom's office said in a statement.

"Warnings delivered through the system are based on a computerized program called ShakeAlert operated by the US Geological Survey that analyzes data from seismic networks in California, calculates preliminary magnitudes, and then estimates which areas will feel shaking," the statement said.

The new app was put to the test this week before its official launch when two earthquakes struck in the San Francisco area and central California, measuring 4.5 and 4.7 respectively. Residents who had the app were alerted within an average of 2.1 seconds in the first case and 1.6 seconds in the latter.

Newsom said that the system was not perfect but would improve over time.

Officials warned that in rare circumstances, residents may receive a ShakeAlert when there is no quake taking place.

Seismologists say that California is long overdue for a huge earthquake, dubbed the Big One, as the state straddles one of the country's most dangerous fault lines -- the San Andreas fault.