Karen Gemmell of Motion Entertainment said the mist machine had been tested all week and it was a technical error on the day that set the fire alarm off.
She said the mist elevated, got trapped, and tripped the alarm.
"It was an issue that hadn't come up during our testing but we are aware of all fire safety and standards."
Ms Gemmell said everyone cleared out and the building was given the go-ahead by fire services within 20 minutes.
Julian Dennison, the young boy in Hunt for the Wilderpeople, who was there to cut the ribbon, entertained children outside and prize giveaways continued outside.
"Otherwise everyone is having an amazing time, it's all go," Ms Gemmell said.
Rotorua Daily Post photographer Stephen Parker said there was a long queue of people waiting to get in at 10am when the centre was due to open to the public for the first time.
He said the ribbon cutting ceremony was held and most people went inside.
Then within about five minutes, an alarm started going off. Everyone was evacuated and moved away from the building.
Two fire trucks attended.
The multi-million dollar entertainment complex included a Dialled Indoor tramp park, Strike Zone tenpin bowling, Megazone laser tag, Timezone, Escape Masters, Lumberjax mini golf and Chipmunks Playland and Cafe.
