Democratic US presidential candidate Joe Biden and new running mate Kamala Harris have made their first joint appearance on the campaign trail.

Mr Biden said Ms Harris was "the right choice" to help him kick Donald Trump out of the White House.

In a high school gymnasium in his hometown of Wilmington, Delaware, Mr Biden praised his running mate as an experienced and accomplished governing partner who would help him deliver on his campaign agenda.

"I have no doubt that I picked the right person to join me as the next vice president of the United States of America, and that is Senator Kamala Harris," Mr Biden said, introducing her on stage.

"She's ready to do this job on day one. We're both ready to get to work rebuilding this nation," he told supporters.

Accusing President Trump of failing to lead during the coronavirus crisis, Mr Biden said that he and Ms Harris would fix "the mess that President Trump and Vice President Pence have created at home and abroad".

The Democrat said Ms Harris' historic role as only the third woman ever picked for the vice presidency by a major party was inspiring "little girls" across America.

In her speech, Ms Harris declared that the United States was "crying out for leadership".

"The case against Donald Trump and Mike Pence is open and shut," said the former California attorney general.

As the first woman of colour to be a presidential running mate for a major US party, Ms Harris said the US, in particular, needed to face up to the enduring problem of racism.

"We're experiencing a moral reckoning with racism and systemic injustice that has brought a new coalition of conscience to the streets of our country demanding change," she said.

The joint appearance came just days before Mr Biden will formally accept the Democratic presidential nomination at next week's party convention, which will take place largely as a virtual event because of the coronavirus pandemic.

The Republican convention, where President Donald Trump is set to be nominated to seek a second four-year term, follows a week later and kicks off a ten-week sprint to the 3 November election.

Ms Harris, the 55-year-old US senator from California, was announced as Mr Biden's choice after a selection process that drew extra scrutiny thanks to Mr Biden's age.

The 77-year-old former vice president would be the oldest president ever if he wins, raising speculation that he would not seek re-election in 2024.

Ms Harris, the first Black woman and the first Asian American to appear on a major-party US presidential ticket, is the daughter of two immigrants, her mother from India and her father from Jamaica.