The prospect of a victory for Donald J. Trumpin the American presidential election sent global financial markets plunging on Wednesday, as Wall Street futures tumbled as much as 5 percent and Asian stocks sold off sharply.
Investors reacted in real time to early results and predictions showing unexpected gains for Mr. Trump in battleground states, as he appeared closer to pulling off a shocking upset.
Stock market futures pointed to a sell-off looming on Wall Street, with futures on the Dow Jones industrial average falling more than 4 percent. Futures on the broader Standard and Poor’s 500-stock index fell by the 5 percent limit before recovering somewhat.
Markets in Tokyo, Hong Kong, Australia and other countries across the region had fallen by as much as 6 percent by early afternoon. The dollar weakened broadly.
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Oil futures fell sharply as investors worried about the impact of new trade friction on global economic growth. Gold, popular among some investors during uncertain economic times, staged a rally.
Markets around the world had mostly priced in a win by Hillary Clinton in recent weeks, in line with most data-based prediction models. But as the election results trickled in, most models swung from predicting a Clinton win to predicting a win by Mr. Trump, the Republican nominee.
In Japan, economic officials said they were convening an emergency meeting in response to the swings in financial markets. The Nikkei 225 stock index was down nearly 6 percent late in the Tokyo trading day, while the yen — considered a safe haven by some investors — was up by around 3 percent against the dollar. The officials, from the Finance Ministry, the Bank of the Japan and the Financial Services Agency, said they would meet at 3 p.m. Japan time, or 1 a.m. Eastern. In the past, Japan has sometimes intervened in the currency market to curtail sharp upswings in the yen.
Given that the polls were still fairly close before the elections, a Trump victory would not come as a complete surprise, “but it’s still a big shock,” said Shane Oliver, the head of investment strategy and chief economist at AMP Capital in Sydney.
“Share markets across the Asian region have sold down heavily as investors worry in particular that his protectionist policies will kick off a trade war and depress growth,” Mr. Oliver said.
Trading seesawed, tracking live election returns for battleground states like Florida and Ohio as they swung toward Mr. Trump.
“We’ve seen reactions to swings back and forth from Hillary to Donald,” Stephen Innes, a senior currency trader at Oanda in Singapore, said in a phone interview, referring to the nominees, Mrs. Clinton and Mr. Trump.
Mr. Trump’s policies have also irked America’s biggest trading partners. For example, his bold threats to impose steep punitive tariffs on imports from China have raised concerns among leaders in Beijing. But they could also complicate monetary policy making in the United States.
“A Trump presidency means a weaker dollar, and a higher likelihood the Fed would delay a rate hike in December,” said Julian Evans-Pritchard, China economist at Capital Economics in Singapore.
But that could also relieve some of the pressure on China’s currency, which has weakened to six-year lows this year in the face of steady outflows.
Mr. Trump in recent months has repeatedly accused China of intervening to weaken its currency. But this is not correct. Instead, China’s central bank, the People’s Bank of China, has been spending hundreds of billions of dollars of its foreign reserves to prevent the renminbi from weakening. Mr. Evans-Pritchard said a win by Mr. Trump and the resulting weaker dollar “also takes some pressure off” China’s central bank.
The steep sell-off on Wednesday followed a spell when investors around the world appeared to have been on edge over the United States election.
In recent weeks, in tune with what appeared to be the improving fortunes of Mr. Trump, the markets took on a darker tone as retail investors pulled money out of equity funds and institutional players unloaded some of their riskier investments such as high-yield bonds.
Last week, for example, investors pulled $3 billion out of junk bond exchange-traded funds, the largest weekly outflow all year.
The prospects of a Trump victory seemed to brighten after James B. Comey, director of the Federal Bureau of Investigation, told Congress on Oct. 28 that the agency was examining newly discovered emails from a laptop computer belonging to the estranged husband of a top aide to Mrs. Clinton, the Democratic nominee. Stocks slumped after the news. For the next nine trading days, stocks closed lower, the first such losing streak since 1980.
On Monday, stocks rallied after Mr. Comey said the emails warranted no further actionfrom the F.B.I. The Standard & Poor’s 500-stock index closed 2.2 percent higher and edged up 0.4 percent on Tuesday.
Over the last three months, the S.&P. index was down 2.5 percent, while the price of gold, traditionally seen as a safe harbor in uncertain times, was up almost 3 percent.
The Chicago Board Options Exchange Volatility Index, or VIX, which is known as Wall Street’s “fear gauge,” rose in late October to its highest levels since the market turmoil that followed Britain’s vote to leave the European Union in June.
The Mexican peso has experienced the brunt of the market’s ups and downs related to Mr. Trump. While the peso has lost 10 percent of its value against the dollar over the last year, the swings have been wild.
Whenever Mr. Trump gained ground against Mrs. Clinton, the currency would plunge up to 7 percent against the dollar, only to snap sharply back as Mrs. Clinton pushed ahead. Some 80 percent of Mexico’s exports go to the United States, and the peso is one of the world’s easiest currencies to trade, making it a popular gauge of market sentiment regarding Mr. Trump’s chances.
The dollar has gained on the pound since Britain’s vote to split from Europe, while it has remained flat for the year against the euro and the Japanese yen.
But perhaps the most noticeable trend of the last few months has been the slow but persistent increase in the interest rates of government bonds, many of which have been in negative territory for some time.
The yield on the benchmark 10-year United States Treasury note rose to 1.86 percent on Tuesday from a low of 1.37 percent in July.
Analysts suggest that this trend may well reflect nascent signs in the developed economies of inflation and increased economic activity.
A view is also taking hold that the next president of the United States is going push hard for an increase in government spending as a way to spur what has been a stagnant economic recovery, and both candidates have spoken out in favor of such an approach.
Any move toward a meaningful pickup in infrastructure investing would require more government borrowing and thus put upward pressure on today’s rock-bottom interest rates.
Last week, the former United States Treasury secretary Lawrence H. Summers made the case, in a speech at the International Monetary Fund, that with rates at historically low levels and with the increasing chances of the economy entering a recession in the coming years, more government spending is desperately needed.
“The question of lack of demand should be our preoccupation in thinking about macroeconomic policy going forward,” Mr. Summers said. “And it has a natural solution — issuing debt to support whatever investments the government sees as best.”
Governments around the world that are sitting on large piles of cash, Germany for example, are facing similar pressures to take advantage of low rates to borrow and spend to stimulate a more vigorous level of growth.
While such policies would also increase debt levels, economists who support Mr. Summers’s policy prescription argue that a trade-off of higher growth is worthwhile, given how low borrowing costs are right now.