Ms Field said such incidents were taken seriously. It was believe the fire was started with a lighter.
"[Residents] are not allowed to smoke while at a facility and tobacco and lighters are banned," Ms Field said.
"Staff do all they can to make sure contraband does not make its way into any youth facility, but unfortunately some residents are determined and go to extreme lengths to conceal banned items."
A Rotorua Fire Service spokesman said firefighters were called to the facility about 10.15am.
"There was a small fire in one of the bedrooms there," he said. "It was only small and it was put out by the staff before we arrived."
The $47 million facility takes up to 30 young offenders from around the Bay of Plenty and Waikato.