US Democrats on Tuesday nominated Joe Biden as their 2020 presidential candidate, formally designating the Washington veteran as the party's challenger to incumbent President Donald Trump in the November election.

In an unprecedented roll call vote that took place entirely online due to the coronavirus pandemic, all 50 states and seven territories announced their vote tallies that cemented Biden's role as the party flagbearer.

"Well thank you very, very much, from the bottom of my heart," a beaming Biden said in a live video link as he celebrated the nomination.

Former US First Lady Michelle Obama
Former first lady Michelle Obama said "Donald Trump is the wrong president for our country". Photo: DEMOCRATIC NATIONAL CONVENTION / Handout

"It means the world to me and my family," he added, reminding viewers he will deliver a formal acceptance speech on Thursday at the conclusion of the four-day jamboree.

The nomination was a formality as he had already won the majority of the more than 3,900 delegates back in June.

The roll call came on Day 2 of the mostly virtual Democratic National Convention aimed at celebrating the party's candidate and welcoming independents and frustrated Republicans into their political movement to oust Trump from the White House.

US President Donald Trump
US President Donald Trump lashed out at former first lady Michelle Obama after she delivered a scathing takedown of his leadership. Photo: AFP / MANDEL NGAN

The proceedings included a series of presentations by party leaders past and future who unleashed their own arguments against the White House incumbent and urged voters to rally around Biden.

The lineup featured president Jimmy Carter, who served one term from 1977, and 1990s commander-in-chief Bill Clinton, who warned that the Trump White House is swirling with chaos instead of the competence necessary to address the nation's crises.

"At a time like this, the Oval Office should be a command center. Instead, it's a storm center. There's only chaos," Clinton said.

Former US First Lady Michelle Obama
IMAGES AND SOUNDBITES"Donald Trump is the wrong president for our country," former first lady Michelle Obama says in a keynote speech on the first night of the Democratic convention that has shifted entirely online due to the coronavirus pandemic. Photo: POOL

"Just one thing never changes -- his determination to deny responsibility and shift the blame," Clinton said. "The buck never stops there."

The president faced a barrage of criticism on opening night too, most notably from former first lady Michelle Obama who said Trump lacks the character and skills for the job.

"I thought it was a very divisive speech, extremely divisive," Trump told reporters at the White House.

Eva Longoria was the emcee
Actress Eva Longoria served as the emcee on the opening night. Photo: DEMOCRATIC NATIONAL CONVENTION / Handout

In her pre-taped remarks to the convention, Obama urged Americans to rally behind Biden, her husband's former vice president, in the November 3 presidential election.

Trump's White House is marred by "chaos, division and a total and utter lack of empathy," Barack Obama's wife said in unprecedented criticism of a sitting US president by a former first lady.

"Donald Trump is the wrong president for our country," she added. "He is clearly in over his head."

Former US President Bill Clinton
Former US president Bill Clinton is to address the second night of the Democratic convention. Photo: GETTY IMAGES NORTH AMERICA / POOL

Later Tuesday on a visit to battleground state Arizona, Trump knocked Obama for delivering taped remarks.

"Thursday night I'm doing it live," Trump said, referring to his speech next week when he formally accepts his party's nomination at the Republican convention, which has also shifted online.

Trump said he has chosen the White House South Lawn as the location, after saying in recent weeks that he would pick between the presidential mansion and the historic battlefield at Gettysburg.

Delivering such an obviously political speech from the White House will stir substantial controversy, as presidents are required to separate their campaigning from taxpayer-funded governing.

In addition to Clinton and Carter, Tuesday's lineup featured Jill Biden, who has been married to the candidate since 1977.

The educator from Pennsylvania, who served eight years as second lady, has campaigned at length for Biden, repeatedly speaking of his values and commitment to everyday Americans.

The educator from Pennsylvania delivered a personal, high-stakes prime-time testimonial about her husband, including how the personal tragedy of the death of his first wife and daughter in a 1972 car crash has shaped him.

"How do you make a broken family whole?" she said. "The same way you make a nation whole. With love and understanding -- and with small acts of compassion. With bravery. With unwavering faith."

The camp is promoting Joe Biden as a unifier. In their appeal to middle-of-the-road voters and frustrated Republicans the convention featured a video of the unlikely friendship between Biden and late Republican senator John McCain, narrated by his widow Cindy McCain.

Republican former secretary of state Colin Powell also delivered videotaped remarks in which he endorsed Biden and said he shared the Democrat's values.

Tuesday's keynote was notable in that it featured 16 mostly young current and former elected Democrats seen as upcoming leaders including Stacey Abrams, who spent time as a Georgia lawmaker.

Former president Obama will speak on Wednesday along with 2016 Democratic presidential nominee Hillary Clinton and Biden's running mate, Senator Kamala Harris of California.

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