U.S. equity futures plunged by more than 1.6%, or 500 Dow points after President Trump confirmed through a tweet that he and the first lady tested positive for coronavirus.
Dow futures are down 1.3%, or 360 points.
The S&P 500 is down 1.4%, or 46 points. The Nasdaq is declining by 1.9%, or 220 points.
The Dow Industrials had only been down 50 points before the announcement.
"Tonight, @FLOTUS and I tested positive for COVID-19," the president wrote. "We will begin our quarantine and recovery process immediately. We will get through this TOGETHER!"
“To say this potentially could be a big deal is an understatement,” Rabobank said in a commentary. “Anyway, everything now takes a backseat to the latest incredible twist in this US election campaign.”
In Asia, Japan's Nikkei ended the trading session down 0.8%, after returning from a day in which that market saw its trading day halted following a technical failure.
Markets in Hong Kong and China were closed for a second day due to holidays.
European markets have opened lower following the news. London's FTSE is down 1.1%, Germany's DAX is declining 1.2% and France's CAC fell 1.0%
Gold is trading down $2.30 at $1,914.20.
In energy markets, U.S. crude is down 4.3%, or $1.69 at $37.05. Brent crude is also off 4.3%, or $1.74 at $39.19.
The president and first lady’s positive coronavirus tests came just hours after news surfaced that senior White House adviser Hope Hicks tested positive for COVID-19.
In a statement, White House spokesman Judd Deere said the president “takes the health and safety of himself and everyone who works in support of him and the American people very seriously.”
“White House Operations collaborates with the Physician to the President and the White House Military Office to ensure all plans and procedures incorporate current CDC guidelines and best practices for limiting COVID-19 exposure to the greatest extent possible both on complex and when the President is traveling,” Deere said.
The Associated Press contributed to this article. Get updates on this story from FOXBusiness.com