Washington: A COVID-19 vaccine is "ready" and coming "within weeks" and would be distributed by the military, US President Donald Trump said on Thursday while his Democratic challenger Joe Biden alleged that America is about to enter into a dark winter as they clashed over their policies on the pandemic during the final presidential debate.

The 90-minute debate, just less than two weeks ahead of the crucial presidential election on November 3, started in Nashville, Tennessee, with opening remarks by both the candidates, when the mike of the other was muted to avoid interruptions.

The coronavirus dominated the opening minutes of the Trump-Biden face-off with President Trump terming the contagion a worldwide problem.

We have a vaccine that's coming. It's ready, it's going to be announced within weeks and it's going to be delivered, Trump, 74, said adding that companies like Johnson & Johnson, Moderna and Pfizer are doing very well on that front.

We also have others that we're working on very closely with other countries, in particular, Europe, he said.

Asserting that his timeline is going to be more accurate, Trump said he has his generals lined up for the fast distribution of the vaccine, as he expects to have 100 million vials.

As soon as we have the vaccine, he (general) is ready to go, said the president, who is seeking re-election.

Former vice president Biden, 77, challenged Trump and alleged that his policies have resulted in a large number of deaths in the country.

We are about to go into a dark winter. A dark winter and he has no clear plan and there's no prospect that there's going to be a vaccine available for the majority of the American people before the middle of next year, Biden said.

According to Johns Hopkins coronavirus tracker, the coronavirus has so far infected more than 41 million people and killed over 1.1 million people globally. The US is the worst affected country with over 8 million cases and 223,000 deaths.

Trump has often said that the worst is over with the pandemic. During the debate he reasserted this, claiming the US was rounding the turn, we've rounded the corner. But the latest numbers show a rise in cases and hospitalisations in the US. Around 60,000 new daily coronavirus cases are being reported across the US, up from around 50,000 a day at the beginning of October, according to the Covid Tracking Project.

Trump said: I don't know if we're going to have a dark winter at all. We are opening up our country. We've learned and studied and understood the disease, which we didn't at the beginning. When I closed and banned China from coming in, heavily infected, and then ultimately Europe, but China was in January months later, he was saying I was xenophobic. I did it too soon".

Biden said: He is xenophobic, but not because he shut down access from China. And he did it late, after 40 countries had already done that. In addition to that, what he did, he made sure that we had 44 people that were in there in China trying to get to Wuhan to determine what exactly the source was.

What did the president say in January? He said 'no', he said he's being transparent. The president of China is being transparent. We owe him a debt of gratitude. We have to thank him then what happened was we started talking about using the Defense Act to make sure we go out and get whatever is needed out there to protect people.

Biden said: He (Trump) had nothing. He did virtually nothing and then he gets out of the hospital and he talks about this don't worry. It's all going to be over soon. Come on. And there's not another serious scientist of the world who thinks it's going to be over soon.

Trump said that the country is learning to live with it.

We have no choice. We cannot lock ourselves up in a basement like Joe does. He has the ability to lock himself up. I don't know. He's obviously made a lot of money someplace. But he has this thing about living in the basement, he said.

The president said that he cannot afford to live in a basement, like his Democratic challenger.

I'd love to put myself in the basement or in a beautiful room in the White House and go away for a year and a half until it disappears. I can't do that. Every meeting I had, every meeting met a lot of families, including Gold Star families and military families I said this is dangerous. And you catch it. And, you know, I caught it. I learned a lot, great doctors, great hospitals.

And now I recovered... 99.9 per cent of young people recover. Ninety-nine per cent of people recover. We have to recover. We can't close up our nation. We have to open our school. And we can't close up our nation or you're not going to have a nation, Trump said.

Biden, referring to New England Medical Journal, said the way this president has responded to this crisis has been absolutely tragic.

I will take care of this. I will end this. I will make sure we have a plan, he said.

Trump said that his administration closed up the greatest economy in the world in order to fight this horrible disease that came from China.

It's a worldwide pandemic. It's all over the world. You see the spikes in Europe and many other places right now. If you notice, the mortality rate is down 85 per cent. The excess mortality rate is way down and much lower than almost any other country, and we are fighting it, and we are fighting it hard, he said.

Noting that more and more people are getting better, Trump said that this is a worldwide problem.