President Donald Trump and his challenger Joe Biden have fiercely clashed in one of the most chaotic and rancorous presidential debates in years.

Amid angry shouting and name calling, the two fought over the Covid-19 pandemic, white supremacy and the economy, as the moderator, Fox News anchor Chris Wallace, struggled to maintain control of the 90-minute forum in Cleveland, Ohio.

In a vitriolic back and forth punctuated by insults, Biden, 77, told Trump, 74: "You're the worst president America has ever had."

Biden called the president a "clown" and told him to "shut up".

Trump brought up drug use by his rival's son.

Interrupting Biden nearly every time he spoke, Trump made little attempt to reassure swing voters about his leadership.

Biden hit back: “This is so unpresidential.”

The debate focused on six topics in 15-minute segments - the candidates' records, the Supreme Court, the pandemic, race, election integrity and the economy

Due to the pandemic, the debate at Case Western Reserve University had a small, socially-distanced audience and the traditional opening handshake was skipped.

The two candidates are scheduled to meet next in two weeks, on 15 October, for the second debate in Salt Lake City, Utah.

Opinion polls suggest Biden has a steady single-digit lead over Trump.

But with 35 days until Election Day, surveys from several important states show a closer contest.