Three disco balls that formed part of an exhibition were stolen from Queenstown Gardens on Saturday night or early on Sunday morning.
Festival chairman Duncan Forsyth described the thieves as "mongrels".
"A whole lot of people couldn't fully enjoy it [the exhibit]," he said.
The mirrorballs were on loan, so the cost of replacing them would have to come out of the donations people made during the festival, he said.
That would be between $200 and $300.
"So many people come to enjoy it, and a couple of mongrels ruin it," Mr Forsyth said.
"We want to make it super accessible. We don't want to have to rope exhibits off."
He said the odd person became a bit "exuberant", but the festival usually only had minor damage or a few missing fairylights.
"Not something as deliberate as this."
Mr Forsyth is appealing for the return of the mirrorballs, or any information about their whereabouts.
