Billionaire Tesla CEO Elon Musk has proposed acquiring Twitter by buying all the shares of the US social media giant he does not already own.

Musk revealed his offer in a post on his Twitter account on Thursday.

A US Securities and Exchange Commission filing shows that Musk has proposed purchasing all the remaining stock of Twitter for 54.20 dollars per share. The offer is estimated to be worth about 43.3 billion dollars.

Musk had earlier bought a 9.2 percent stake in Twitter, making him its largest shareholder. But he had declined to join the board of directors.

Musk said in a letter to Twitter's board of directors that he believes in the company's potential to be the platform for free speech around the world. He added Twitter will not ''serve this societal imperative in its current form'' and it needs to be transformed as a private company.

He said he will ''unlock'' the company's potential.

Twitter confirmed that it had received the offer from Musk.

The company said its board of directors "will carefully review the proposal to determine the course of action that it believes is in the best interest of the Company and all Twitter stockholders."