GETTYSBURG (AFP) - White House hopeful Joe Biden warned on Tuesday (Oct 6) that "the forces of darkness" are dividing Americans, stressing that as president he would strive to "end the hate and fear" consuming the nation.

In a speech at the site of the famous Civil War battle of Gettysburg, the Democratic challenger to President Donald Trump in November's election condemned the rise of white nationalism and said the country needed to unite.

"The forces of darkness, the forces of division, the forces of yesterday are pulling us apart, holding us down and holding us back," Biden said in a speech near where president Abraham Lincoln delivered his inspirational Gettysburg Address during a cemetery dedication here in 1863.

"We cannot and will not allow extremists and white supremacists to overturn the America of Lincoln and (abolitionists) Harriet Tubman and Frederick Douglass, to overturn the America that has been a haven and a home for everyone no matter their background," Biden added.

The 77-year-old, who leads in polling four weeks from election day, made no mention of Trump's name, but the Democrat's remarks notably came one week after the president failed to directly condemn white nationalism during their contentious debate in Cleveland.

"I do not believe we have to choose between law and order and racial justice in America. We can have both," Biden said. But he stressed that "as president... I will send a clear unequivocal message to the entire nation: There is no place for hate in America. It will be given no license, it will be given no oxygen, it will be given no safe harbour."

His speech was intended to serve as a call for unity after months of bitter divisions, but he also said he was "concerned" about what he sees today.

"The country is in a dangerous place, our trust in each other is ebbing, hope seems elusive," and politics is no longer a forum for mediating differences but a battleground for "total, unrelenting partisan warfare," he said.

The veteran Democrat repeatedly invoked the language of Lincoln in his speech, saying "there's no more fitting place than here today, in Gettysburg, to talk about the cost of division."

"Today once again, we are a house divided. But that, my friends, can no longer be," Biden said.