Two teenagers were forced to remove their outer clothing before they were attacked by a group of six people.
The assault occurred on Wednesday at 8.30pm as two young men were relaxing in their car in the carpark opposite Bluewater Stadium after attending a sports game.
The were approached by up to six males who were described as being in their mid 20s, Maori and wearing dark colours.
One was said to be wearing a black bandana.
One of the victims had their cellphone taken before the group left in several vehicles.