Kamala Harris a powerful voice for US: Joe Biden

Democratic Party's presidential nominee Joe Biden has said that his running mate, Kamala Harris will make a "great Vice President" with a powerful voice for the nation.

In his speech on Thursday night while formally accepting his nomination at the last day of the Democratic National Convention, he spoke of her various identities that mesh with the party's assertions of unity and empowerment of minorities.

Outlining his monumental tasks ahead if he is elected, Biden said: "I won't have to do it alone. Because I will have a great Vice President at my side. Senator Kamala Harris. She is a powerful voice for this nation.

"Her story is the American story. She knows about all the obstacles thrown in the way of so many in our country. Women, Black women, Black Americans, South Asian Americans, immigrants, the left-out and left-behind.

"But she's overcome every obstacle she's ever faced. No one's been tougher on the big banks or the gun lobby. No one's been tougher in calling out this current administration for its extremism, its failure to follow the law, and its failure to simply tell the truth."

While accepting her nomination for Vice President on Wednesday, Harris paid tributes to her mother, Shyamala Gopalan, and her activism as an immigrant.

Harris said she stood on the shoulders of her mother and promised to be "committed to the values she taught me".

Harris spoke of her family that included her sister, niece, stepchildren, uncles and "chithis" (younger maternal aunts).

Biden said on Thursday that "Kamala and I both draw strength from our families. For Kamala, it's (husband) Doug (Emhoff) and their families. For me, it's Jill and ours."

"No man deserves one great love in his life. But I've known two," Biden said recalling his late first wife Neilia.

"After losing my first wife in a car accident, Jill came into my life and put our family back together.

"And I will have the strength that can only come from family. (Son) Hunter, (daughter) Ashley and all our grandchildren, my brothers, my sister. They give me courage and lift me up," he said.

He also mentioned his other son Beau, who had died as an adult because of a brain tumour.

"While he is no longer with us, Beau inspires me every day," he said.