MSCI's broadest index of Asia-Pacific shares outside Japan dropped 0.4 percent while Japan's Nikkei fell 1.1 percent.
Asian shares stumbled and the US dollar was on the defensive on Wednesday as signs that Republican US presidential candidate Donald Trump could be closing the gap with his Democratic rival Hillary Clinton spooked investors.
Anxiety in markets has deepened over a possible Trump victory given uncertainty on the Republican candidate's stance on several issues including foreign policy, trade relations and immigrants, while Clinton is viewed as a candidate of the status quo.
In the currency market, traders sold the dollar partly as they suspect Trump would prefer a weaker dollar given his protectionist stance on international trade.
The euro rose to a three-week high of USD 1.1069, up about two percent from its 7-1/2-month low of USD1.0851 hit just over a week ago. Against the yen, the dollar slipped to 104.03 yen from three-month high of 105.54 yen set on Friday.
"If you had a long dollar position on the view that the dollar would gain because Clinton would win, you would surely close that position because her victory is less certain," said Koichi Yoshikawa, executive director of financial markets at Standard Chartered Bank.
