Tesla chief Elon Musk sold nearly US$4 billion worth of shares in the electric car company, SEC filings showed, more than a week after he closed his US$44 billion acquisition of Twitter.

Musk has been pushing for ways to pay for the massive deal, for which he took on billions of dollars in debt and earlier sold US$15.5 billion worth of shares in Tesla.

On Tuesday, documents filed with the US Securities and Exchange Commission (SEC) indicated that he had disposed of more than another 19 million shares, worth in excess of US$3.9 billion.

Musk took control of Twitter and fired its top executives in late October, after a drawn-out back-and-forth between the world's richest person and the influential social media company.

The billionaire initially tried to step back from the deal after his unsolicited offer was accepted in April.

He said in July that he was cancelling the contract because he had been misled by Twitter over the number of fake "bot" accounts, allegations rejected by the company.

After Musk sought to terminate the sale, Twitter filed a lawsuit to hold the entrepreneur to the agreement. With a trial looming, he revived his takeover plan.

On Friday, Twitter sacked half of its 7,500-strong staff as its new owner launched an overhaul of the company.

Jack Dorsey, who co-founded Twitter in 2006 and stepped down as CEO last year, tweeted to apologise for growing the site too quickly, following news of the firings.

Musk has been searching for ways for the social media platform to make money after the buyout, including an idea to charge users US$8 a month for verified accounts.

The move would help overcome a potential loss of advertisers, Twitter's main source of revenue, after many top brands put their ad buys on hold following Musk's pledge to dial back content moderation on the site.

Musk's actions and statements since taking over the reins of Twitter have prompted concern, including warnings from the United Nations.

UN rights chief Volker Turk has urged Musk to make respect for human rights a priority for the social network.

Musk has insisted that content moderation remains a priority for Twitter and that he would create a council dedicated to the task. (AFP)