Police were called to a Whangarei supermarket after a crowd of youths gathered outside the store while others looted items from inside.
Police said they were called to Countdown Okara at about 9.30pm on Saturday following reports of about 100 young people congregating outside.
A police spokesman said while the large group stood outside another smaller group entered the store and stole items.
A nearby fireworks display at Toll Stadium, which was attended by about 10,000 people, had just ended when the incident happened.
Police said two people were arrested and CCTV from the store would be reviewed.
