A handful of tweets and four days later, Silicon Valley billionaire Elon Musk has closed orders for his latest novelty product, after selling 20,000 flamethrowers at $500 a piece.

"Guaranteed to liven up any party!" was Musk's tagline for a sale which raised $10 million for his high-speed tunnel venture The Boring Company.

The new product officially sold out Thursday, Musk said on Twitter.

The man behind electric carmaker Tesla and rocket company SpaceX had earlier sold 50,000 Boring Company hats in similar fashion.

The latest impromptu fundraising scheme comes at a time when financial analysts and investors in Tesla are wondering if Musk will have to seek billions more in funding for the electric carmaker as it struggles to meet promises on production.

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