Tesla Inc boss Elon Musk has disclosed a 9.2 per cent stake in Twitter Inc, worth nearly $US3 billion ($A4.0 billion), making him the micro-blogging site’s largest shareholder and triggering a rise of more than 27 per cent in the company’s shares.

Musk’s move, revealed in a regulatory filing, comes on the heels of his tweet that he was giving “serious thought” to building a new social media platform, while questioning Twitter’s commitment to free speech.

In a Twitter poll on Monday, Musk asked users if they want an edit button, after disclosing the stake. On April 1, Twitter tweeted a message on its official account, saying it was working on an edit button.

A prolific Twitter user, Musk has over 80 million followers since joining the site in 2009 and has used the platform to make several announcements, including teasing a go-private deal for Tesla that landed him in hot water with regulators.

Of late, however, the world’s richest person has been critical of the social media platform and its policies, and recently ran a Twitter poll asking users if they believed the platform adheres to the principle of free speech, to which over 70 per cent voted no.

Twitter’s recent quarterly results and lower-than-expected user additions have raised questions about its growth prospects, even as it pursues big projects such as audio chat rooms and newsletters to end long-running stagnation.

Musk – who, according to Forbes, has a net worth of about $US300 billion ($A398 billion) – has been reducing his stake in Tesla since November, when he said he would offload 10 per cent of his holding in the electric-car maker. He has already sold $US16.4 billion ($A21.7 billion) worth of shares since then.

A regulatory filing on Monday showed that Musk owns 73.5 million Twitter shares, which are held by the Elon Musk Revocable Trust, of which he is the sole trustee. Vanguard is Twitter’s second-biggest shareholder, with an 8.79 per cent stake, according to Refinitiv data.

Twitter shares rose 27.1 per cent on Monday to close at $US49.97 ($A66.27). The stock, which had fallen 38 per cent in the past 12 months through Friday’s close, on Monday added as much as $US8.38 billion ($A11.11 billion) to its market capitalisation, which now stands at $US39.3 billion ($A52.1 billion).

Twitter did not immediately respond to a request for comment on Musk’s move.

Get all the latest Canberra news, sport, entertainment, lifestyle, competitions and more delivered straight to your inbox with the Canberra Daily Daily Newsletter. Sign up here.