The Democrats in the U.S. have officially nominated Joe Biden as their presidential nominee, in the November election designating the veteran leader as their challenger to President Donald Trump.

Because of the coronavirus pandemic all 50 US states and seven territories announced their tallies endorsing Biden in a virtual roll call vote on Tuesday.

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

"It means the world to me and my family," he said, telling viewers he would give a formal acceptance speech on Thursday at the end of the four-day Democratic National Convention.

Biden's election was a formality because he had already secured the bulk of the more than 3,900 delegates back in June.


The convention included presentations by Democrats, including former Presidents Jimmy Carter, 95, and Bill Clinton, 74.

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

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

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

After Biden formally became a nominee, his wife, Jill Biden, addressed the nation for the first time as the prospective first lady.

Jill, who holds a doctorate in education, gave impassioned remarks about the closure of schools across the US and the loss of lives due to the pandemic.

She recounted her life with Joe in the aftermath of the death of his first wife and daughter in a car crash in 1972 and testified to his strength of character following his son Beau's death from cancer in 2018.

"There are those who want to tell us that our country is hopelessly divided, that our differences are reconcilable but that is not what I see over these last few months," Jill said.

"We just need leadership worthy or our nation and worthy of you, honest leadership to bring us back together to recover from this pandemic and prepared for whatever else is next."

After her remarks, Joe called his wife: "The love of my life and the rock of our family."