The ABC News/Washington Post tracking poll - which was dismissed as "bad polling" - suggested Trump had a 46 per cent lead over Clinton, whose chances have fallen seven points to 45 per cent since the FBI launched a new investigation into how she stored emails during her time as secretary of state.
China's blue-chip CSI300 fell 1.7 per cent to 3,220 points, while the Shanghai Composite fell 1.8 per cent to 2,980 points.
Meanwhile, the Nikkei 225 ended the day 1.7 per cent lower, at 17,134 points.
"Since the FBI reopened its case into Clinton’s emails last Friday, her substantial lead in the polls has been decimated, said Craig Erlam, senior market analyst at Oanda.
"It’s been clear for some time now that markets would much prefer the stability that a Clinton victory would bring for the US economy and the reaction over the last 24 hours or so since the polls started to change so dramatically just confirms this. Trump risk is well and truly being priced in again.
But he pointed out that other factors may be at play.
The sell-off in equity markets is not being helped by sharp declines in crude prices in recent days. As cracks in the Opec production agreement have started to appear, it has become clear that markets bought into this way too early and now they’re starting to correct themselves."