A grievous assault involving dirt-bike riders in East Auckland has prompted a warning from the local board and police. 

Footage circulating online shows a motorist being cut off and swarmed at the intersection of Pakuranga and Fortunes Roads - and getting attacked as he tried to get away.

Howick Local Board Chair Bruce Kendall says this is a symptom of an international phenomenon of people being reckless.

"They end up in a bit of a mob mentality and they end up doing some pretty bad things. And I don't know how this situation got to this particular point - I've only seen the video from the point that the car is stopped...and it looks pretty dangerous to me." 

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