Former US Vice-President and Democratic White House front-runner Joe Biden has been slammed by Senator Kamala Harris, who is of Indian and Jamaican descent, for his record on race in a televised debate and challenged on his previous comments about segregationists.

The debate on Thursday night came a day after the first batch of the 10 presidential hopefuls squared off in an event hosted by television network NBC in Miami, as the party decided to divide the field of 20 candidates into two groups of 10.

The debate – the second over two days to accommodate the huge field of candidates vying for the Democratic nomination – saw Biden face off against Vermont Senator Bernie Sanders, the US media reported.

The dramatic moment of the evening came in response to a question about race and policing, when Harris interjected, saying that she had a right to respond as the only black candidate on stage.

She then directed her comments to Biden, denouncing his record on race. “I do not believe you are a racist,” Harris said, looking directly at the former Vice-President.

“But,” she continued, “it is personal and it was actually hurtful to hear you talk about the reputations of two US senators who built their reputations and career on the segregation of race in this country.”

Her attack was a reference to a remark Biden made recently on the campaign trail in which he spoke fondly of his relationship with segregationist senators. When called upon by his rivals to apologize, he refused, Efe news reported.

Harris also accused Biden of supporting policies that would have prevented young minority students like herself from attending school in white majority districts. She said when he opposed bussing, there was a little black girl in Oakland, California, who was being bussed to a better school.

“There was a little girl in California who was part of the second class to integrate her public schools and she was bussed to school every day,” Harris said. “That little girl was me.”

Biden sought to defend his record, saying he was only against “busing ordered by the Department of Education” but didn’t oppose local integration efforts, and tried to put his comments about former Senate colleagues in context.

“It’s a mischaracterization of my position across the board. I did not praise racists,” he said.

Biden drew criticism last week when he referred to the two racist Southern senators when speaking of a time when the Senate could achieve “civility”.

The candidates also criticized President Donald Trump and sparred over racial issues, the scope of healthcare policies and the universality of government assistance programmes.

Thursday’s stage featured Biden, Sanders, Harris, South Bend Indiana Mayor Pete Buttigieg, New York Senator Kirsten Gillibrand, Colorado Senator Michael Bennett, former Colorado Governor John Hickenlooper, California Representative Eric Swalwell, activist and author Marianne Williamson and tech entrepreneur Andrew Yang.

The common denominator between all candidates was a withering criticism of Trump’s actions in his time in office, as well as their rejection of the tax cut package passed by the Republican-dominated Congress in 2017 that benefited the wealthiest segments of the American society and is estimated to carry a loss of $1.5 trillion to US coffers.

Biden also faced challenges from a new generation of presidential hopefuls who took aim at his decades-long record as a Delaware senator and questioned whether the party’s Obama-era policies have gone far enough in achieving progressive goals.

The arguments pivoted over the role of government in healthcare and other issues – and whether the party should embrace aspects of democratic socialism, a position repeatedly pushed by Sanders.

Two of Biden’s chief rivals — Sanders and Massachusetts Senator Elizabeth Warren — have advocated steep tax increases for the wealthy and corporations to fund their sweeping plans for an expansive healthcare system, college affordability and safeguards against climate change.

The two rounds of debates were held ahead of Sunday’s second-quarter fundraising deadline, which may yield more clarity on the candidates’ viability as their totals trickle out ahead of a July 15 reporting deadline.