U.S. Vice President Kamala Harris delivered a concession speech to the nation on Wednesday after a whirlwind campaign that failed to stop Republican Donald Trump's return to the White House.

"While I concede this election, I do not concede the fight that fueled this campaign," she told supporters, many of them in tears, at her alma mater Howard University, a historically Black college in Washington.

Harris pledged to continue fighting for women's rights and against gun violence and to "fight for the dignity that all people deserve."

She said she had called President-elect Trump, congratulated him on his triumph and promised to engage in a peaceful transfer of power.

The somber mood was in striking contrast to the homecoming a few weeks ago on the Howard campus when thousands of students and alumni gathered ahead of what they hoped would be the election of the country's first graduate of historically Black Colleges and Universities as president.

Harris addressed a crowd that included former House Speaker Nancy Pelosi, aides in President Joe Biden's White House and thousands of fans. Harris' campaign anthem, Beyonce's "Freedom," played as she entered the stage.

Her running mate, Minnesota Governor Tim Walz, joined the crowd.

Harris encouraged her supporters, especially young people, not to give up even in their disappointment.

"Sometimes the fight takes a while. That doesn't mean we won't win," she said.

Harris rose to the top of the Democratic ticket in July after Biden stepped aside and brought new-found enthusiasm and cash to the Democratic ticket, but she struggled to overcome voters' concerns about the economy and immigration.

She was handed a resounding loss on Tuesday, with Trump winning a greater share of votes across most of the country compared with his performance in 2020 and Democrats failing to secure key battleground states that decide elections.

Thousands had gathered at the school on Tuesday night for what they hoped would be a historic victory for the first woman to become president. They came back on Wednesday to show their support after her loss.

"I'm here today to show love and respect for her ... for what she's done," said Donna Bruce, 72. Bruce said she had just seen a little girl with a T-shirt that said: "A Black girl will save the world."

"I still believe that," Bruce said. "It may not be this Black girl, but I believe a Black girl will."