California voters are set to decide on a billionaire wealth tax that could pave the way for a national levy

Analysts say the vote is being watched closely in Washington as a test of whether voters will support taxing unrealised capital gains and large fortunes directly.

If passed, the measure would mark the first state-level wealth tax of its kind in the US, targeting billionaires and those with assets above a set threshold.

Critics warn the tax will accelerate California's already rapid exodus of high-net-worth residents and businesses, deepening the state's fiscal problems rather than solving them.

Backers see a 'yes' vote as the opening move in a campaign to bring a national wealth tax to Congress.