U.S. stock index futures were sharply lower Wednesday triggered by worries over the looming "fiscal cliff" and as fears over Europe resurfaced, trumping an initial relief from President Barack Obama's re-election.

"I don't think there's a long-term market reaction to the presidential election itself—it's now how quickly we can focus on the 'fiscal cliff' and coming up with a resolution," said Art Hogan, managing director of Lazard Capital Markets. (Read More: For Investors, More Fed Easing, Cliff 'Heart Attack' Await)

Meanwhile, ratings agency Fitch said Obama needs to move quickly to avoid the "fiscal cliff" that is threatening the country's economic recovery, adding that failure to address the issue would likely result in a downgrade in 2013.

However, the dollar fell against other major currencies, on worries over the "fiscal cliff" and continued monetary expansion. Gold, copper and other commodity prices rose on the weakness in the greenback.

Obama was re-elected president Tuesday night, put over the top by the crucial battleground state of Ohio following the most expensive election in U.S. history.