A white supremacist wearing a swastika armband in Seattle was tracked down and knocked out after allegedly harassing a black man on a bus.

The unidentified Nazi was first spotted on Sunday afternoon while riding Seattle's D line bus where witnesses claimed he had been harassing another passenger.

A photo of him sitting on the bus was quickly passed on to several anti-fascists who then used their Twitter and Facebook accounts to track him down in less than 90 minutes.

A man wearing a swastika armband in Seattle was tracked down and knocked out on Sunday after allegedly harassing a black man on a bus

He was eventually found on a street corner in downtown Seattle where he was filmed getting into a confrontation with several unidentified people.

Footage of the ordeal, which surfaced online moments later, showed the Nazi being struck directly in the face by a man wearing a gray sweatshirt.

Moments before he was hit, he could be heard yelling: 'They deserve welfare.'

After being knocked to the ground with a single punch, another man could be heard saying to him: 'Night, night.'

One of the social media users who tracked the white supremacist congratulated the person who threw the punch.

When anti-fascists were able to track him down to a Seattle street corner, footage showed him being punched directly in the face

The man was knocked to the ground with a single punch and struggled to get back up again

A photo of him sitting on the bus was quickly passed on to several anti-fascists who then used their Twitter and Facebook accounts to track him down in less than 90 minutes

'I would say that we successfully identified, tracked and coordinated to neutralize a clear and present danger to Seattle,' he told BuzzFeed.

'Whether we coordinated the actual punch or not… I, for one, applaud the anonymous hero.'

Seattle Police said they received reports of a man wearing a swastika armbands and instigating fights on Sunday afternoon.

'Police were on the scene in five minutes and found him on the ground. He declined to provide info about the incident and left after removing his armband,' police said.

'No one else at the scene contacted officers to make a report about the incident.'