Stock index futures came well off session lows after Hillary Clinton conceded the presidential election to Donald Trump. Dow futures were about 190 points lower after earlier falling 800 points. Stock futures fell and bonds rallied as markets feared Donald Trump could pull off an upset and take the White House. Just before midnight ET, S&P 500 futures and Nasdaq 100 futures plunged more than 5 percent. Around 8:03 a.m. ET, they held about 23 points lower and 76 points lower, respectively. That was just above levels identified as "limit down" by the CME, which confirmed to CNBC that S&P and Nasdaq futures can trade above but not below those prices until 9:30 a.m., ET, when the Wednesday U.S. trading session begins. Trade volume in eMini S&P futures was about 17 times the average daily volume, according to a note from Citi.

Investors moved into the safety of bonds Tuesday evening as traders questioned whether Democrat Hillary Clinton could still win the race. The Mexican peso briefly fell more than 10 percent against the U.S. dollar.

"Right now, the markets are heading for the hills, but we'll see," said Robert Tipp, chief investment strategist, global bonds and foreign exchange at Prudential Fixed Income. "That's a function of fear as much as fact." Tipp said it's not clear whether Trump would be as disruptive as the markets worry he could be, since it's unclear what parts of his platform would be pursued and what type of individuals he would choose for his Cabinet. U.S. futures were volatile as election results started rolling out at around 7 p.m. ET. Dow futures were up as much as 100 points at one point before turning south as state after state were projected to have picked Trump. Keith Parker, global equity strategist at Barclays who studied what might happen if Trump were to win, projected the S&P 500 could move initially to around 2,000, if the Republican businessman prevails. The S&P 500 ended Tuesday's session higher, up 8 at 2,139, as markets speculated that Clinton was in the lead. "Markets would be volatile. Equities would take their cue from confidence indicators — what Trump says, what the GOP leadership does," he said. Trump was the projected winner in some important battleground states, including Florida and North Carolina, but others remained too close to call. While the winner has yet to be determined, Trump appeared to be on the verge of a stunning victory.