Tesla CEO Elon Musk has sold another significant portion of his shares in the electric car manufacturer, according to regulatory documents released on Friday.

The billionaire sold about 640,000 Tesla shares, valued at about $ 687 million, according to the records. Earlier this week, Musk sold approximately $ 5 billion worth of shares.

In total, Musk sold 5.1 million shares worth around $ 5.69 billion this week. The transactions accounted for around 3% of its stake in Tesla, according to Reuters.

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TSLATESLA, INC.985.87-47.55-4.60%

Musk still holds more than 167 million Tesla shares following the latest transactions. Tesla’s market capitalization is more than $ 1 trillion.

Tesla shares fell almost 3% in trading on Friday. The company’s stock is down about 10% this week, though shares are still up more than 40% so far this year.

The sell-off began earlier this week after Musk posted a Twitter poll asking his followers if he should sell 10% of his Tesla stock. Musk has announced that he will use a portion of his proceeds to cover his tax liability from stock options exercised.

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According to Forbes, Musk is one of the richest people in the world with a net personal worth of more than $ 271 billion.

The Associated Press contributed to this report.