U.S. President Donald Trump said on Friday that he and his wife Melania had tested positive for COVID-19 and were going into quarantine, upending the race for the White House.

"We will begin our quarantine and recovery process immediately. We will get through this TOGETHER!" the president said in a late night tweet.

Trump, 74, is at high risk for the deadly virus both because of his age and because he is considered overweight. He has remained in good health during his time in office but is not known to exercise regularly or to follow a healthy diet.

The results came after news that Hope Hicks, a top adviser and trusted aide, had tested positive for the new coronavirus earlier on Thursday.

Trump, who is tested regularly for the virus that causes COVID-19, has held rallies with thousands of people in recent weeks in the run-up to the Nov. 3 election, despite warnings from public health professionals against having events with large crowds.

The president largely eschews wearing masks and has criticized others who do. Public health professionals say mask-wearing is key to helping to prevent the virus from spreading.

Trump's positive test caps a months-long response to the virus, the seriousness of which he has consistently underplayed. Earlier on Thursday night the president predicted that the end of the pandemic was in sight.

The development alters the presidential race dramatically.

The White House issued a new schedule for Trump's activities on Friday that did not include his planned trip to Florida. Trump has held regular rallies around the country to drum up enthusiasm for his candidacy against Democratic rival Joe Biden, who is ahead in national opinion polls.

Trump has come under sharp criticism for his response to the coronavirus pandemic that has killed more than 200,000 people in the United States alone. The president has touted his management of the crisis.