US stock index futures have tumbled as the path to victory for market favourite Hillary Clinton narrowed after Ohio was called for Republican Donald Trump, putting him on a stronger course to win the US presidential election.
Trump and Democratic rival Clinton remained in close battles not only in traditional battleground states, but also in some states expected to have been in Clinton's column like Michigan and Wisconsin.
Some networks called Florida and North Carolina for Trump.
Financial markets reacted violently to the results, with S&P futures down more than four per cent and Dow Industrials futures falling more than 700 points.
Wall Street has seen former Secretary of State Clinton as a status quo candidate who would lend stability to the markets, while Trump's stances on foreign policy, trade and immigration are seen sparking volatility.
At 1413 AEDT S&P 500 e-minis were down 97.5 points, or 4.57 per cent, with 1,086,214 contracts changing hands. Nasdaq 100 e-minis were down 217.25 points, or 4.52 per cent, in volume of 144,332 contracts, and Dow e-minis were down 684 points, or 3.74 per cent, with 188,215 contracts changing hands.
"Nobody had hedged for a Trump win so people are trying to get out as quickly as possible now," said Paul Nolte, portfolio manager at Kingsview Asset Management in Chicago. "A lot of people are making big assumptions now based on the early returns. In my mind its preliminary."
CBOE Volatility index futures shot nearly 40 per cent higher, reflecting investors' reservations over a Trump presidency.
The Mexican peso slumped versus the US dollar to a historic low above 20 per dollar. The peso was last down more than 10 per cent against the greenback.
"Big surprise, clearly going into the evening the polls were within the margin of error in most cases, but at the same time the general expectation was not that Trump would be victorious," said David Joy, chief market strategist at Ameriprise Financial in Boston.
"There are still votes to count, but the way the night is unfolding is a surprise so far, and you are seeing that reflected in these asset prices."
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