California's Secretary of State Alex Padilla gave the green light on Thursday for proponents of "California Nationhood" -- also known as Calexit -- to start collecting the nearly 600,000 signatures needed for the measure to qualify on the November 2018 ballot.

The 585,407 signatures required by July 25 represent eight percent of registered voters in California -- the most populous state in the country with nearly 40 million residents and the world's sixth-largest economy.

Should the initiative make it on the ballot, a "Yes" vote would repeal clauses in the California Constitution "stating California is an inseparable part of the United States and that the United States Constitution is the supreme law of the land," a statement by Padilla's office said.

Voters would then need to decide in another referendum in 2019 whether California should become a separate country.