'Will you shut up?': Donald Trump and Joe Biden bicker during debate

Americans could barely believe what they were seeing as today's debate between Donald Trump and Joe Biden turned extraordinarily ugly.

The first US presidential debate turned extraordinarily ugly today, as Donald Trump and Joe Biden hurled insults and repeatedly spoke over each other.

The two candidates have been slagging each other off in public for months, but this was their first face-to-face meeting, and it quickly went off the rails.

Moderator Chris Wallace struggled to maintain control as Mr Trump in particular repeatedly interrupted both he and Mr Biden.

"I guess I'm debating you, not him. That's OK, I'm not surprised," the President remarked at one point, addressing Wallace.

You can read all about the key moments in our blog below.

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When the debate ended and the US TV networks cut back to their studios for analysis, several of the anchors and political experts seemed shellshocked by what they had just witnessed.

NBC anchor Lester Holt, who has moderated presidential debates in the past, described it as a "low point in American political discourse".

"Frankly, I'm a bit at loss for words here to describe what we've just witnessed," Holt said.

"I think we just need to pause for a moment and say, that was crazy. What was that?" said his colleague Savannah Guthrie.

Over on ABC, George Stephanopoulos said he had never seen a worse debate in his life.

"I have to speak personally here, as somebody who's watched presidential debates for 40 years, as someone who has moderated presidential debates, as someone who has prepared candidates for presidential debates," said Stephanopoulos.

"That was the worst presidential debate I have ever seen in my life."

The network's White House correspondent, Jon Karl, agreed that the debate was "a total mess".

They were even harsher on CNN.

"That was the worst debate I have ever seen. It wasn't even a debate. It was a disgrace," said anchor Jake Tapper.

He labelled it "a hot mess inside a dumpster fire inside a trainwreck".

"That was a s***show," said his colleague Dana Bash.

"That is really the phrase I'm getting from people on both sides of the aisle on text, and it's the only phrase I can think of to describe it."

It was certainly unlike any other debate I've witnessed. Read on for all the highlights - and lowlights.