Staff in darker parts of the Emergency Department, which has many curtained-off cubicles, used their phones or torches to assist the emergency lighting.
Patient monitors worked on batteries. However, electronic patient boards and computers operating the electronic transfer of patients could not be used during the outage.
Lines company Unison and the DHB are investigating the incident.
Dr Snee said it was important for both organisations to have a clear understanding of what had happened, because of the possible compromise of the "effective and safe operation" of the hospital and the risk to equipment.
The DHB had been reassured it was a rare event and unlikely to happen again, he said. Staff had coped well and managed the difficult situation "with patient safety being the priority".
"It was a good reminder to everyone that we need to be prepared and have well-understood contingencies in place for when power is lost, as we never know when that may be," he said.
All areas of the hospital had contingency plans and battery power took over lifesaving equipment.
Unison customer care manager Danny Gough said only the hospital suffered the power outage. "It is very concerning to both us and the hospital and we are working closely with them," he said.
Investigations by both organisations were ongoing, with investigators reporting to the DHB's executive management team yesterday.
