Democratic US vice presidential nominee, Kamala Harris has reacted after US President Donald Trump and his campaign promoted a birther conspiracy against her last week.

Last week, former Vice President Joe Biden selected Harris as his running mate, boosting his chances of defeating Trump in the November polls.

If Biden is elected, Harris would be the first Black and South Asian American vice president.

After Biden announced Harris as his running mate, John Eastman, a lawyer and Chapman University professor questioned Harris' eligibility to contest for president or vice president in a Newsweek op-ed, saying she was born to Indian and Jamaican parents.

Harris was born in Oakland, California, making her natural born citizen meaning she is eligible to be vice president, but Trump, who has pushed similar conspiracies about former President Barack Obama, said that he would not be "pursuing" questions about Harris' eligibility, but did not dismiss the conspiracy theories as false. Instead he praised the lawyer John Eastman as "very highly qualified" and a "brilliant lawyer."

Trump also said he heard on "social media" that Harris could be ineligible but he won't be focusing on it.

"I know nothing about it, but it's not something that bothers me," the President said during a news conference at his Bedminster, New Jersey, golf club. 

"I just don't know about it but it's not something we will be pursuing."

Harris has now responded to the birther theories saying Trump's campaign will "engage in lies" and "deception" but she is ready for the attacks.

"They're going to engage in an attempt to distract from the real issues that are impacting the American people. And I expect that they will engage in dirty tactics. And this is going to be a knockdown, drag-out. And we're ready," Harris told media outlet TheGrio in an interview released Sunday August 16, when asked how Trump promoting birther conspiracies signals the tactics his campaign will use.