NASHVILLE (REUTERS) - United States President Donald Trump and Democratic challenger Joe Biden offered sharply contrasting views on the still-raging coronavirus pandemic at Thursday's (Oct 22) final presidential debate, seeking to persuade the few remaining undecided voters 12 days before the Nov 3 election.

Mr Trump, a Republican, adopted a more restrained tone than he did during the chaotic first presidential debate in September, which was quickly derailed by his constant interruptions.

But Thursday's clash still featured plenty of personal attacks between two men who evidence little respect for each other, and Mr Trump kept fact-checkers busy by levelling unfounded corruption accusations at Mr Biden and his family.

The absence of disruptions yielded a more substantive debate over a range of topics including the economy, race, climate change, healthcare and immigration.

But the coronavirus, which has killed more than 221,000 people in the United States, loomed over the proceedings as it has throughout the campaign.

The televised encounter in Nashville, Tennessee, represented one of Mr Trump's last remaining opportunities to reshape a race that national opinion polls show he has been losing for months, though the contest is much tighter in some battleground states likely to decide the election.

"Anyone who's responsible for that many deaths should not remain president of the United States of America," Mr Biden said.

"We're about to go into a dark winter. A dark winter. And he has no clear plan."

Trump, who has put his stewardship of the economy at the centre of his campaign, defended his approach to the outbreak and said the country could not afford to close businesses again despite fresh surges.

"We're learning to live with it," said Mr Trump, who has played down the virus for months. "We have no choice."

"Learning to live with it?" Mr Biden retorted. "Come on. We're dying with it."

Mr Trump asserted that a vaccine was potentially "weeks" away.

Most experts, including administration officials, have said a vaccine is unlikely to be widely available until mid-2021.

Opinion polls show most Americans disapprove of the President's response to the virus.

Several US states, including the election swing state of Ohio, reported record single-day increases in Covid-19 infections on Thursday, evidence the pandemic is accelerating anew.

Mr Trump, whose instinct remains to run as an outsider, portrayed Mr Biden as a career politician whose nearly 50-year record was insubstantial.

But did not lay out a clear agenda for the second term while Mr Biden returned again and again to Mr Trump's nearly four years as president, pointing to the economic damage the virus has done to people's lives.

He also faulted Mr Trump for avoiding responsibility for the pandemic.

"I take full responsibility," Mr Trump responded. "It's not my fault that it came here, it's China's fault."

After an opening segment on the pandemic, Thursday's clash pivoted to rapid-fire exchanges over whether either candidate had improper foreign entanglements.

Mr Trump repeated his accusations that Mr Biden and his son Hunter engaged in unethical practices in China and Ukraine.

No evidence has been verified to support the allegations, and Mr Biden called them false and discredited.

Mr Trump's effort to uncover dirt on Mr Hunter Biden's Ukraine business ties led to the President's impeachment.

Mr Trump and his children have been accused of conflicts of interest of their own since he entered the White House in 2017, most involving the family's international real estate and hotel businesses.

Mr Biden defended his family and said unequivocally that he had never made "a single penny" from a foreign country, before pivoting to accuse Mr Trump of trying to distract Americans.

"There's a reason why he's bringing up all this malarkey," Mr Biden said, looking directly into the camera. "It's not about his family and my family. It's about your family, and your family's hurting badly."

He also accused Mr Trump of skirting his taxes, citing a New York Times investigation that reported Mr Trump's tax returns show he paid almost no federal income tax over more than 20 years.

"Release your tax returns or stop talking about corruption," Mr Biden said.

Mr Trump, who has broken with decades of precedent in refusing to release his tax returns, said he had paid "millions".

He again said he would release his returns only once a longstanding audit was completed.

The candidates clashed over healthcare, China policy and - after months of anti-racism protests - race relations, with Mr Biden saying Mr Trump was "one of the most racist presidents" in history.

"He pours fuel on every single racist fire," he said. "This guy has a dog whistle as big as a foghorn."

Mr Trump responded by criticising Mr Biden's authorship of a 1994 crime Bill that increased incarceration of minority defendants while asserting that he had done more for black Americans than any president with the "possible" exception of Abraham Lincoln in the 1860s.

Mr Biden criticised Mr Trump's effort to persuade the US Supreme Court to invalidate the Affordable Care Act, the sweeping healthcare reform passed when Mr Biden was vice-president in President Barack Obama's administration.

"People deserve to have affordable healthcare, period," he said, noting that the law prevented insurance companies from denying coverage to people with pre-existing conditions.

Mr Trump said he wanted to replace the ACA with something "much better" that would offer the same protections, even though the administration has yet to propose a comprehensive healthcare plan despite a promise to do so for years.

During a segment on climate change, Mr Biden said his environmental plan would "transition from the oil industry" in favour of renewable energy sources, prompting Mr Trump to go on the attack.

"He is going to destroy the oil industry," he said. "Will you remember that, Texas? Will you remember that, Pennsylvania?"

Biden said he simply wanted to eliminate federal subsidies for oil companies, a point he reiterated to reporters following the debate. "We're not getting rid of fossil fuels for a long time," he said.

Relatively few voters have yet to make up their minds, and Mr Trump's window to influence the outcome may be closing.

A record 47 million Americans already have cast ballots, eclipsing total early voting from the 2016 election.

The contentious first debate, when the two men traded insults, was watched by at least 73 million viewers.

Mr Trump passed up another planned debate last week after it was switched to a virtual format following his Covid-19 diagnosis.

On Thursday, the commission that oversees the debate removed plexiglass barriers separating the candidates after Trump provided proof he had tested negative for Covid-19, a source familiar with the matter said.

The commission also muted the candidates' microphones to allow each to deliver two-minute statements on each new topic before turning them back on, in an effort to avoid the chaos of the first debate.

The approximately 200 attendees had their temperatures checked before entering the venue, and everyone was required to wear a medical mask at all times.