The crash, involving a car and motorcycle, happened on State Highway 1, Burnham, south of the city, shortly before 10pm on Friday.
Several patched Mongols members were quickly on the scene.
The motorcyclist, Steve Smith, an associate of the gang, died.
It’s thought they’d been riding in convoy.
On Saturday, Smith’s partner posted a tribute on social media, describing him as “the most amazing dad” and “our rock”.
“I’m so thankful to love you and share the most precious memories with you,” she said.
The Mongols, an infamous international bikie gang, established a New Zealand chapter in the Bay of Plenty in 2019.
Early last year it expanded into Canterbury, where it set up a headquarters in Burnham.
The gang has many members who have been deported from Australia in recent years.
Its arrival in New Zealand has led to tension in the underworld, including fire bombings and tit for tat shootings.
An investigation into the cause of the Burnham crash was ongoing, police said on Saturday.
SH1 was closed between Aylesbury Rd and Dunns Crossing Rd following the crash.