Democratic presidential nominee Joe Biden has said that if he is elected in the November 3 election, he will make Covid-19 vaccines free for all Americans.

"Once we have a safe and effective vaccine, it has to be free to everyone -- whether or not you're insured," Xinhua news agency quoted Biden as saying during a speech in Wilmington, Delaware, on Friday.

He once again slammed President Donald Trump for his response to the coronavirus pandemic, saying he has "given up" fighting the virus and has "quit on America".

The former Vice President made the pledge a day after he debated Trump for the last and final time before the November 3 election.

The coronavirus pandemic was a central topic at the debate.

"Covid-19 dwarfs anything that we've faced in recent history, and it isn't showing any signs of slowing down," said Biden, adding that the virus, which has now killed more than 223,000 people nationwide, "is surging in almost every state".

"We're more than eight months into this crisis and the president still doesn't have a plan," said the 77-year-old.

He also laid out his pandemic response plan if elected, which includes consultation with governors of all the 50 states during the presidential transition period; a national mask mandate in all federal buildings and on all interstate transportation; and an increase in daily testing reaching seven times today's level.

Trump, during the debate the previous night, boasted about a vaccine that is coming "within weeks," only to backtrack when pressed by the moderator, saying his statement was not a "guarantee".

Biden's remarks on Friday came as the US is trying to battle a resurgence of fresh coronavirus cases.

Presently the worst-hit country in the world by the pandemic, the US has so far reported 8,484,991 Covid-19 cases and 223,914 deaths.