Joe Biden promised Thursday to end the "darkness" of Donald Trump's presidency in a speech accepting the Democratic nomination with an impassioned call for unity and a return to optimism.

"The current president has cloaked America in darkness for much too long. Too much anger, too much fear, too much division," Biden said.

"If you entrust me with the presidency, I will draw on the best of us, not the worst. I will be an ally of the light, not the darkness," he said.

"It's time for us, for we the people, to come together."

Speaking in his hometown of Wilmington, Delaware, but with an audience almost entirely online or on television, Biden's acceptance speech reflected the enormity of the shutdown that has upended life across the United States in the battle against the deadly coronavirus.

And Biden, 77, urged Americans in blistering terms to punish Trump for the chaos that has seen more than 170,000 deaths and economic calamity.

"We lead the world in deaths," he said in the 22-minute speech, calling Trump's performance "unforgivable."

"On day one" of his own presidency, Biden said, he would implement a national COVID-19 plan and mandate mask wearing.

Biden is on his third White House bid after failing to win the nomination in 1988 and 2008.

But after months of relentless mockery from Trump and other Republicans who claim Biden is senile, the veteran politician's speech was markedly fluent and always full of passion.

Democrats hope the strong performance, as well as the vice presidential nomination of Kamala Harris -- the first black woman ever to make it onto the White House ticket of a major party -- will deflate those attacks.

- Trump hits Pennsylvania -

Biden leads in almost every national opinion poll and also in the crucial swing states.

But Trump is fighting hard in what is shaping up to be an election of unprecedented ferocity and division.

Speaking to Fox News's Sean Hannity as the Democratic convention was in full swing, Trump repeated his claim that increased mail-in voting -- which Democrats say is needed due to coronavirus fears -- will lead to fraud.

"They're trying to steal the election," said Trump, who has pointedly refused to confirm that he will accept the result if he loses.

Earlier, Trump also tried to overshadow Biden's thunder with a visit just outside his challenger's birthplace in Scranton, Pennsylvania.

In a dark speech, Trump falsely claimed that Biden had abandoned the blue collar town -- he in fact moved out with his family when he was a child -- and warned that Democrats would usher in an era of "violent mobs" and "blood-stained sidewalks."

Pennsylvania is exactly the kind of place that used to be reliably Democratic but is now divided, with many seduced by Trump's economic nationalism and vows to defend traditional white, working class values.

The state will be fiercely contested on November 3.

- Unified Democrats -

Trump's shock win in 2016 over Hillary Clinton was partly helped by divisions within the Democrats. This time, the party is doing everything to emphasize unity, with many of Biden's primary rivals appearing in a friendly joint video call during the convention.

One by one, guests ranging from comedian Julia Louis-Dreyfus to Democratic heavy hitters came out to rip Trump, while praising Biden's ability to connect with people who are suffering at a time when the country is going through twin health and economic crises.

"Joe Biden cares," said a 13-year-old boy, who movingly recounted to the convention how he overcame stuttering thanks to encouragement from lifelong stutterer Biden.

If that was the most raw, emotionally wrenching moment, former New York mayor and billionaire entrepreneur Mike Bloomberg landed one of the sharpest punches against the Democrats' nemesis Trump.

"Would you rehire or work for someone who ran your business into the ground?" Bloomberg asked, addressing small business owners around the country.

Senator Tammy Duckworth, a badly wounded Iraq war veteran, branded Trump the "coward in chief" who lets "tyrants manipulate him like a puppet."

That was a point Biden then echoed, saying that under his administration the days of the United States "cozying up to dictators is over."