Washington,  A former aide to US Vice President Mike Pence has slammed President Donald Trump's handling of the Covid-19 pandemic, and said she will vote for Democratic presidential nominee Joe Biden in the November 3 election.

Olivia Troye, Pence's former lead staff member on the White House Coronavirus Task Force which is headed by the Vice President, made her case against Trump in a video ad for the "Republican Voters Against Trump" group, Xinhua news agency reported on Friday.

"Towards the middle of February, we knew it wasn't a matter of if Covid-19 would become a big pandemic here in the US, it was a matter of when," Troye said in the ad. 

"But the President didn't want to hear that because his biggest concern was that we were in an election year and how is this going to affect what he considers to be his record of success?

"It was shocking to see the president saying that the virus was a hoax, saying that everything is OK when we know that it's not. The truth is he doesn't actually care about anyone else but himself.

"At some point I would come home at night. I would look myself in the mirror and say, 'Are you really making a difference? Does it matter?' Because no matter how hard you work and what you do, the President is going to do something that is detrimental to keeping the Americans safe," she said.

Troye added that although she has been a Republican her entire life, she will vote for Biden because she truly believes Americans are "at a time of constitutional crisis."

In response, Pence told reporters at the White House on Thursday: "it reads to me like one more disgruntled employee who's left the White House decided to play politics during an election year. 

"I couldn't be more proud of the work we've done."

Also responding to the video, White House spokesperson Judd Deere said in a statement: "Outside of generally watching the White House Coronavirus Taskforce from the overflow staff room, this disgruntled former detailee was never in private meetings with the President and her assertions have no basis in reality and are flat out inaccurate.

"The truth is President Trump always put the well-being of the American people first as evidenced by his shutdown of the country, which saved millions of lives, activating the greatest mobilization of the private sector since World War II to deliver critical supplies, the development of a never-before-seen testing system that is the envy of the world, and an unending focus on the rapid research and approval of scientifically proven therapeutics and an eventual vaccine."

As of Friday, the US is still the worst-hit country with the world's highest number of cases and deaths at 6,674,070 and 197,615, respectively, according to the Johns Hopkins University.