The US Democratic presidential candidate Joe Biden has tested negative for the coronavirus, hours after President Donald Trump revealed he tested positive.

"Vice President Joe Biden and Dr. Jill Biden underwent PCR testing for COVID-19 today and COVID-19 was not detected. I am reporting this out in my capacity as both Vice President Biden and Dr. Biden's primary care physician," said Dr. Kevin O' Connor.

The Biden campaign said the former vice president and his wife, Jill Biden, were both tested Friday morning out of an abundance of caution.

During the presidential debate Tuesday in Cleveland, Biden was in the same room as Trump was for nearly two hours on stage.

Neither man wore a mask on stage, nor did debate moderator Chris Wallace. But Trump and Biden's podiums were placed approximately 8 ft. apart, and they didn't get close to one another. The Centers for Disease Control's current guidance for physical distancing is 6 ft.

Planning for Biden's scheduled trip to Michigan on Friday was fluid for much of Friday morning, as campaign aides processed the news of Trump's diagnosis and determined his next steps.

Biden's running mate, Sen. Kamala Harris left Washington at midday bound for Las Vegas, where she has an event later  Friday.

Harris was tested for COVID-19 on Thursday, and she tested negative, campaign aides said.

Both Biden and Harris sent best wishes to the president and first lady on Friday.

On Friday morning, Biden campaign manager Jen O’Malley Dillon sent an email to staff assuring them that the campaign was taking every health precaution to protect Biden, Harris and their families. She also asked them not to post on social media about Trump's diagnosis without prior approval.

The email, which was obtained by NBC News, underscores the political sensitivity of the president's diagnosis in the context of the presidential race.

(With input from agencies)