LOS ANGELES (DPA) - Former US Vice-President and Democratic front runner Joe Biden called President Donald Trump "despicable" on Thursday (July 18) for his racist remarks about four Democratic congresswoman of colour.

At a breakfast event with more than three dozen black community leaders and restaurant workers at Dulan's in South Los Angeles, Biden condemned Trump for appearing to bask in his supporters' "send her back" chants about Rep. Ilhan Omar, D-Minn., at a North Carolina rally last night. Omar, a refugee from Somalia, is a naturalized US citizen who was elected to Congress last year.

"You can imagine if someone said that when I was speaking, what I would have said: 'No. Stop,'" Biden said of the chant when talking to reporters after the breakfast.

"Speak up, man. Not after the fact."

Biden likened Trump to the former Alabama Gov. George Wallace, the last major presidential candidate known for embracing openly racist rhetoric on the campaign trail. And he called for Trump to "outright condemn" racists.

"Let me hear him say 'I condemn them.'"

Trump said on Thursday that he was "not happy with" the chant, yet during the rally, he paused and looked around at the crowd during the shouting, making no attempt to stop it.

Of Trump's backtrack, Biden said: "He does that all the time on everything. ... Look, this is a game. This is about dividing the country, this is about dividing and raising the issue of racism across the country because that's his base, that's what he's pushing."

This week, Trump attacked Omar and three other congresswomen of colour who have been critical of him - Reps. Alexandria Ocasio-Cortez, D-N.Y.; Ayanna Pressley, D-Mass.; and Rashida Tlaib, D-Mich.

He suggested they "go back" to "the crime infested places from which they came." All four are US citizens, and all but Omar were born in the United States.

Democrats, Biden said, "should be the opposite" of Trump.

At the South Los Angeles event, Biden went behind the counter to serve breakfast to community leaders before telling them about the need for criminal-justice reform and economic revitalisation in predominantly black neighbourhoods.

Biden has previously faced criticism from opponents for working with segregationist senators during his long career in the US Senate, but the former vice president for Barack Obama still enjoys strong support among black voters.