Elon Musk has taken the witness stand for a second day in a San Francisco federal court.

The tech billionaire is defending against claims that he defrauded investors when he tweeted on August 7, 2018, that he had "funding secured" to take Tesla private at $US420 per share, and that "investor support is confirmed."

Investors say they lost millions as a result of Musk's tweets.

Tesla's stock price surged after Musk's tweets, and later fell as it became clear the buyout would not materialize.

US Judge Edward Chen ruled last May that Musk's post was untruthful and reckless.

A jury of nine will decide whether the Tesla CEO artificially inflated the company's share price by touting the buyout's prospects, and if so by how much.

Musk did not discuss takeover price with Saudis

On Monday (US time), Musk told the court that he was sure he had backing from Saudi financiers in 2018 to privatise Tesla, but said the fund later backpedalled on its commitment.

The Tesla CEO told the shareholders' lawyer that he met with representatives of Saudi Arabia's sovereign wealth fund (the Public Investment Fund) at Tesla's Fremont, California, factory on July 31, 2018.

Musk acknowledged he did not discuss a takeover price with representatives of the Saudi fund, but said they made clear they would do what it took to make a buyout happen.

"PIF unequivocally wanted to take Tesla private," he testified.

Musk subsequently said that Yasir Al-Rumayyan, governor of the fund, later backpedalled on the commitment to take Tesla private.

"I was very upset because he had been unequivocal in his support for taking Tesla private when we met and now he appeared to be backpedaling," he said at the witness stand.

The shareholders' lawyer told the court that written evidence does not support Musk's claim (that the Saudi fund made a commitment to him).

The lawyer added that minutes of a meeting between Musk and the Saudis showed the Saudis wanted to learn more about the billionaire's plan.