In less than 40 minutes an online fund started by Democrats raised enough money to fix and reopen a firebombed GOP office Sunday.

The speed of the online crowdfund showed "a thirst for civility and democracy," said technologist and Harvard researcher David Weinberger, who writes about the internet's effect on human relationships.

The Republican Party headquarters in Hillsborough, Orange County, North Carolina, were vandalised overnight and the damage discovered early Sunday. The message "Nazi Republicans leave town or else" was spray-painted on the side of a nearby building.

The interior of the office was burned along with the furniture inside, after a bottle containing accelerant was thrown through the front window. Hillsborough police are investigating.

"This is not how Americans resolve their differences," wrote Weinberger, who started the crowdfund. "We talk, we argue, sometimes we march, and most of all we vote. We do not resort to violence by individuals or by mobs."

The Democratic and Republican candidates are working their way across the US as the election campaign enters its final weeks.

Donald Trump will be speaking in Green Bay, Wisconsin, late Monday. Senator Bernie Sanders, Vice Presidential nominee Tim Kaine, and former President Bill Clinton, are all making campaign stops for Hillary Clinton throughout the US. The third Presidential debate is scheduled for Wednesday, October 19.