"Am considering taking Tesla private at $420".
The tweet suggested Mr Musk was looking at a plan to buy outstanding shares in the firm for $420 each, around a fifth higher than the share's current price.
Tesla's shares were up 6.5pc at $363.46. The stock had been up earlier in the day after The Financial Times reported a Saudi Arabian sovereign wealth fund had bought a $2 billion stake in Tesla.
Tesla spokespeople have not yet confirmed the proposal to any media outlets.
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- CBS News' Jillian Harding contributed reporting. Musk previously tweeted an April Fool's joke about his $60 billion company going broke.
Musk has been under intense pressure this year to prove he can deliver on his promise to turn his money-losing company into a profitable higher-volume manufacturer, a goal that has propped up Tesla shares and resulted in a market value higher than that of General Motors Co.
The stock since settled at $366.94 before exchanges halted trading, pending an upcoming announcement from the company. If Musk were to make good on his tweet, it is unclear from where he could secure funding to buy out Tesla's shareholders. Musk's other primary venture, SpaceX, remains privately held. I think he's serious.
"Details, structure, participants and how the valuation has been determined remain to be seen".