Tesla chief Elon Musk stunned investors Tuesday when he tweeted that he was considering taking the company private, sending its stock soaring more than 6 percent.

Musk said he had "funding secured" to take the all-electric automaker private at $420 a share, far above its current $360 stock price. That would value the company — already the United States' most valuable automaker — at more than $70 billion.

Tesla shares were halted around 2 p.m. in advance of pending news.

Musk's tweet was an exceedingly rare way to break potentially monumental news. Public companies often halt trading in their stock and file official releases before making similar statements so as to minimize market jolts and abide by guidance from the Securities and Exchange Commission. The sudden announcement gained immediate criticism from former regulators who suggested it may conflict with SEC rules for potentially market-moving statements.

Harvey Pitt, a former SEC chairman, told CNBC on Tuesday that Musk's tweets "might consittute fraud if any of the facts he disclosed are not true" or if there was any indication that he had floated the proposal purely to boost the stock price.

The company did not immediately respond to requests for comment.

But Musk continued to tweet, adding, "I don't have a controlling vote now & wouldn't expect any shareholder to have one if we go private. I won't be selling in either scenario." Musk also responded "yes" when a Twitter user suggested taking the company private would save "a lot of headaches." He also tweeted that his "hope is *all* current investors remain with Tesla even if we're private."

Musk has long voiced annoyance with the public markets, where the company is beholden to investors and must report quarterly on its losses. The automaker is also the most shorted on Wall Street, with many investors betting the company will fail.

Musk's tweet came shortly after the Financial Times reported the state investment fund of Saudi Arabia had accumulated a stake of up to 5 percent in the company, making it one of Tesla's biggest shareholders.

[Inside the Tesla Factory: Burning cash, and trying not to burn out]

The company said last week that it had burned more than $700 million in cash during the second quarter but made roughly $4 billion in revenue amid increased production of its new Model 3 sedan. Musk said the automaker, which has never made an annual profit, would be profitable by the second half of the year.

Tesla has roughly $10 billion in outstanding debts and about $2 billion in cash reserves, but Musk has asserted in recent months that the company would have no need to raise new funds. "Are we running low on money? The answer is no," Musk told investment analysts last week.

It is far from the first time Musk has dropped a financial bomb to his 22 million Twitter followers. On April Fools' Day, amid growing concerns about the company's cash stockpile, Musk joked via tweets that Tesla had gone "so bankrupt you can't believe it."

Musk — the company's top investor, with more than 20 percent of its shares — has long waged war against the short sellers betting the company's value will plummet. Over the weekend, he tweeted a video parody that cast Adolf Hitler as a short seller flying into a rage at Tesla's recent financial reports. "Dang, turns out even Hitler was shorting Tesla stock …" Musk tweeted.

Musk's other companies specializing in private spaceflight and underground supertrains — SpaceX and The Boring Company — remain private, and Musk has shown reluctance about opening them to the public markets. In 2013, he emailed SpaceX employees that he was "hesitant to foist being public" on the company "given the long term nature of our mission."

The oil-rich kingdom of Saudi Arabia, now led by crown prince Mohammed bin Salman, has shown a key interest in flashy technological investments. The Saudi wealth fund said last year it would invest $1 billion in the private space companies run by Virgin Group founder Richard Branson.