Markets were thrown into disarray as early results from the U.S. election showed Hillary Clinton locked in a tighter-than-anticipated race with Donald Trump in key battleground states.

Panicked traders rushed to unwind bets they piled into over the last two days amid predictions Clinton would sweep to an easy victory. Futures on the S&P 500 erased all of a 2.6 percent rally from Monday and Tuesday that had stood as the third-biggest advance ever in the run-up to election day. Mexico's peso -- a barometer for investors' perceptions of the American vote -- plunged by the most in eight years, while safe-haven demand pushed the yen and gold up by more than 2 percent. Yields on 10-year Treasuries slid to a two-week low.

"It's quite scary," said Nader Naeimi, the Sydney-based head of dynamic markets at AMP Capital Investors, which manages about $125 billion. "The slightest move towards Trump moved the market very quickly. The slightest change in the odds is amplifying market moves and this just shows there's a lot at stake. I don't think it's a done deal yet; at the end of the day we still don't know the winner."

Most polls showed Democratic candidate Hillary Clinton ahead of Trump going into the vote and the first four states to be called were in line with forecasts. At stake is leadership of the world's largest economy at a time when America is divided over immigration, trade and the country's role in the wider world. Websites that take bets on the presidential victor had put the Democrat's odds of winning at 80 percent or more prior to the election.

About 7 million e-minis contracts on the S&P 500 expiring in December have changed hands since the futures market started trading at 6 p.m. New York time, 22 times the average volume at this time of the day over the past month, data compiled by Bloomberg show.

"Trump is getting a greater portion of the results than the polls showed going into tonight," said Chad Morganlander, a money manager at Stifel, Nicolaus & Co. in Florham Park, New Jersey, where he helps oversee about $172 billion. "This is going to be a long night and investors should be prepared for a tremendous amount of market instability over the next several hours"

Among key moves:

--S&P 500 Index futures slide 3 percent

--MSCI Asia Pacific Index drops 1.1 percent, after rising as much as 0.8 percent

--Bloomberg Dollar Spot Index falls 0.1 percent

--Mexican peso tumbles as much as 7.8 percent

--Japanese yen climbs 2.5 percent

--Gold rises 2.1 percent

--Crude oil slides 2.8 percent

--10-year U.S. Treasury yield drops nine basis points to 1.77 percent

---

With assistance from Emma O'Brien Anna-Louise Jackson and Rebecca Spalding