'Nazi Republican' graffiti on office

A North Carolina Republican office has been vandalised with a "flammable material" and graffiti threats telling the "Nazi Republicans" to "leave town or else".

A North Carolina Republican office has been vandalised with a "flammable material", authorities say. (AAP)

The local Republican Party headquarters in Orange County, North Carolina, was struck overnight with a flammable material thrown through a front window of the building, local authorities say.

Someone also spray-painted graffiti including a swastika and the words "Nazi Republicans leave town or else" on an adjacent building, the town of Hillsborough said on its website on Sunday.

"The flammable substance appears to have ignited inside the building, burned some furniture and damaged the building's interior before going out," the statement said.

No damage estimates were yet available.