Democratic presidential nominee Kamala Harris is a “third-rate phoney candidate” and “more incompetent” than her boss President Joe Biden, her Republican rival in the November election, Donald Trump, has said.

In a much-anticipated audio-only interview with billionaire tech magnate Elon Musk on Monday on his social media platform X which was delayed by more than 40 minutes due to technical difficulties, the 78-year-old former president said, “She is a radical left lunatic," as he alleged that “she wants to be more Trump than Trump”.

Launching a scathing attack on the 59-year-old US Vice President, Trump described Harris as a “third-rate phoney candidate.” He reiterated his allegation that Biden being replaced by Harris as a presidential candidate of the Democratic party was a coup.

Musk agreed with the former president and said, "Her behaviour is far left.” "She (Harris) had three and a half years, and by the way, they have another five months that they can do something. But they won't do anything. It's all talk," Trump said.

"She's incompetent, and he (Biden) is incompetent. And frankly, I think that she's more incompetent than he is, and that's saying something because he's not too good," he said.

Trump would face Harris in the general elections on November 5.

He accused Harris of having failed miserably on border security as hundreds and thousands of people entered the country illegally.

Asserting that he is in favour of legal immigration, Trump said it is illegal immigration that he is against.

“She is such a liar,” Trump alleged on X, previously known as Twitter, on the day when he returned to the social media platform.

Over a million people listened to the much-awaited audio-only conversation, which started more than 40 minutes late because of technical issues.

“There appears to be a massive DDOS ( distributed denial-of-service) attack on X. Working on shutting it down. Worst case, we will proceed with a smaller number of live listeners and post the conversation later,” Musk said in a post on X.

During the interview, both Musk and Trump agreed that the crime rate has increased in the US because of the open border policy of the Biden-Harris Administration.

“We're gonna have the largest deportation in the history of this country. And we have no choice,” said the former president.

Responding to a question from Musk, Trump also slammed Biden's foreign policy and applauded Russian President Vladimir Putin, Chinese President Xi Jinping and North Korean leader Kim Jong Un.

“I got along well with them,” he said, claiming there would have been no war if he was the president of the United States.

Meanwhile, Musk stressed that people respond to strength and not weakness and said, “We have some really bad people… we have some really bad people, and I say they are more dangerous than Russia and China.” The biggest threat, he said, is not climate change but nuclear warming.

The conversation between Trump and Musk started with the failed assassination attempt on the former president in Butler, Pennsylvania, on July 13.

“It's very much, I say, an act of God. It's a miracle that it happened,” Trump said.

Commenting on the country's economy, he said the US is having the worst inflation in 100 years. Trump accused the Biden-Harris administration of the worsening of the US economy.

“We need to reduce our government spending. … We need, like a government efficiency commission,” Musk said.

Trump also told Musk, the 53-year-old CEO of Tesla, that he was an “interesting character”.

During the conversation, Trump described China as a primary competitor in Artificial Intelligence and announced that he would close down the Department of Education and move them to the states. In this, he said he would need Musk's help.

Trump, who has 88.8 million followers on X, had 10 posts on the social media platform, each of which has been viewed millions of times.

Some of his posts had 34 million impressions.

His first post, “Are you better off now than you were when I was president? Our economy is shattered. Our border has been erased. We're a nation in decline. Make the American Dream AFFORDABLE again. Make America SAFE again. Make America GREAT Again!” had 25 million impressions.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.