US stock futures and Asian shares fell Friday after President Donald Trump said he and first lady Melania Trump had tested positive for the new coronavirus.
The future contracts for both the S&P 500 and the Dow industrials briefly lost more than 2 per cent but were down 1.4 per cent as of 0630 GMT.
Oil prices tumbled more than 3 per cent.
Trump tweeted news of his test results just hours after the White House announced that senior aide Hope Hicks had come down with the virus after travelling with the president several times this week.
The positive test reading for the leader of the world's largest economy heaps uncertainty onto a growing pile of unknowns investors are grappling with, first among them how it might affect the November 3 election and American policies on trade, tariffs and many other issues beyond then.
"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." Trading in Asia was thin, with markets in Shanghai and Hong Kong closed.
The Nikkei 225 index shed strong early gains, losing 0.7 to 23,029.90 after the Tokyo Stock Exchange resumed trading following an all day outage due to a technical failure.
Reports that the Japanese government is preparing new stimulus measures to help the economy recover from a prolonged downturn worsened by the coronavirus pandemic provided only a temporary lift. Prices fell further after Trump's announcement.
Australia's benchmark S&P/ASX 200 slipped 1.4 per cent to 5,79.50. Shares in Singapore, Thailand and Indonesia also fell.
On Thursday, the benchmark S&P 500 ended the day 0.5 per cent higher, at 3,380.80, the Dow Jones Industrial Average rose 0.1 per to 27,816.90 and the Nasdaq composite rose 1.4 per cent to 11,326.51, as big tech-oriented stocks propped up the market, much as they have through the pandemic.
Such big swings have become typical recently, as investors handicap the chances of a deal on Capitol Hill to send more cash to Americans, restore jobless benefits for laid-off workers and deliver assistance to airlines and other industries hit particularly hard by the pandemic.
House Speaker Nancy Pelosi and Treasury Secretary Steven Mnuchin continued their talks on Thursday, but no breakthrough arrived before stock trading ended on Wall Street. Instead, there were only hopes that were periodically raised and dashed as government officials took turns criticising each other.
"Things remain fluid; we all know what is at stake if this deal does not go through before markets sundown, it is unlikely to be pretty ugly," Stephen Innes of Axi said in a commentary.
Beyond potential political developments, investors will be watching for job figures due out Friday.
Data released Thursday painted a mixed picture for the economy, with one report showing the number of workers filing for unemployment benefits last week fell to 837,000 from 873,000. That was less than economists expected, but incredibly high compared with before the pandemic.
Consumer spending was higher than forecast in August, which is key because it's the main driver of the US economy.
But personal incomes weakened by more than expected last month, and growth in the country's manufacturing sector also fell short of forecasts.
With airlines and other major companies announcing layoffs and furloughs, another round of economic aid from Congress is seen as crucial.
Treasury Secretary Stephen Mnuchin and House Speaker Nancy Pelosi have worked effectively together in the past, helping to drive through the previous economic rescue approved by Congress in March.
But the country's deepening partisan divide has stymied progress, with the presidential election only about a month away.
The yield on the 10-year Treasury fell to 0.66 per cent from 0.67 per cent late Thursday.
US benchmark crude lost USD 1.15 to USD 37.57 per barrel in electronic trading on the New York Mercantile Exchange. It gave up USD 1.50 to USD 38.72 on Thursday. Brent crude, the international standard, lost USD 1.23 to USD 39.70 per barrel.
The dollar weakened to 105.13 Japanese yen from 105.54 yen. The euro weakened to USD 1.1733 from USD 1.1747.
(With input from PTI, ANI)