At 3.45pm, police asked motorists to avoid or delay travel on SH2 near Te Hauke for a couple hours, and for everyone on the roads to "stay patient" as the congestion is managed.
"Police are monitoring behaviour and will follow up with offences detected," the spokeswoman added.
No arrests had been made by 5.30pm.
Police also thanked the public for their patience and understanding.
Police were at 3pm called to a crash on SH2, near Horonui Rd.
Nobody was injured, but one of the vehicles is reported to have fled the scene prior to police arrival.
A police spokeswoman said there is nothing to indicate any of those involved were related to the Mongrel Mob procession.
Police also urged anyone with concerns or information about suspicious or unsafe activity to contact call 111 or 105 to report it.