As it happened: Biden, Trump face off in first presidential debate; Debate gets personal; Economy front and centre

And that is where we will leave it in terms of live coverage. You can find full analysis and reaction at 9news.com.au.

Vice President Kamala Harris has come out swinging in defence of Joe Biden.

Speaking to CNN, Harris acknowledged it wasn't the best performance from Biden.

"It was a slow start, that's obvious to everyone," she said.

"I'm talking about the choice in November.

"Do we want to look at what November will bring, and go on a course for America that is about the destruction of America?"

She noted that Biden is the only candidate who has the endorsement of his vice president.

Mike Pence has said he will not vote for Trump.

President Barack Obama's 2008 campaign manager David Plouffe has described Biden's debate as a "DEFCON 1 moment".

But he said the most important reaction to the debate would be that of voters.

"I have deep suspicion that Donald Trump with swing voters bombed as well," he tol MSNBC.

Scientific polling of the debate performance will not be available for several days.

Prominent Democrats are considering asking Joe Biden to drop his bid for re-election after a disastrous performance, CNN analyst Abby Phillip has said.

"The panic that I am hearing from Democrats is not like anything I have heard," Phillip said.

"There was a deep frustration about Trump's lies."

"Biden's answers were non-coherent."

Joe Biden has centred his closing statement on the cost-of-living relief he passed during his term, and his plans for the next term.

Appearing to search for his prepared talking points, Biden spoke of his tax policy and reduced prices for insulin and prescription drugs.

Donald Trump's closing statement was more freewheeling, speaking about Afghanistan, Israel, Iran, China, Ukraine, Charlottesville, the military, tax cuts, jobs and health care for veterans in the space of two minutes.

Now both candidates are arguing the other would lead the planet into world war three.

"He will drive us into world war three," Trump said.

"We're closer to world war three than anybody can imagine."

Biden hit back.

"You want world war three, let him win and let Putin say, 'Do what you want, NATO'.

"There is a thing called Article 5, an attack on one is an attack on all and requires a response."

Joe Biden has been asked whether he was too old to serve as president.

"I was the second youngest person ever elected to the United States Senate and now I'm the oldest," the 81-year-old said of his 78-year-old opponent.

"This guy is three years younger and a lot less competent."

Trump replied by bragging about acing a cognitive test.

The debate has now descended into a bragging contest about who is better at golf.

"He can't hit a ball 50 yards. He challenged me to a golf match, he can't hit a ball 50 yards," Trump said.

Biden jabbed back.

"I'd be happy to have a driving contest with him. I got my handicap when I was Vice President down to a six.

"By the way, I told you before, I'm happy to play golf if you carry your own bag."

Moderator Jake Tapper has had to ask Donald Trump the same question about drug addiction three times, with the topic not being addressed.

The first time, Trump spoke at length about the American trade deficit with China.

The second time, Trump spoke about drugs crossing the border.

The third time he spoke about his "Remain in Mexico" immigration policy then about a Wall Street Journal reporter being held in a Russian jail.