Police in Finland say they've stopped a far-right terror plot that would have used 3D printed weapons in an attack aimed at leading to the "collapse of society" in a race war.

The National Bureau of Investigation says their initial probe was just looking into a simple firearms offense, but they soon realised there was a bigger issue involving at least four men with links to the far-right.

Local media reports that one of the men in custody had been a municipal election candidate for the Finns Party, which is one of the four parties which makes up the Nordic nation's coalition government.