Ms Wilkie urged people not to go to the emergency department unless their situation was an emergency, because the outage was causing delays in services.
"There will be delays in services while we cannot access our computer system, but in some areas we have been able to revert to manual paper systems. People should go to Lakes Primecare or their family doctor unless it is an emergency."
She said services across the Lakes area, including Taupo Hospital, had been affected, not just those at Rotorua Hospital.
The cause of the fire is unknown, as is when the DHB will be able to get its computer system back up and running.
"We really don't know how long the system will be down. The assessment of the damage is still continuing but it could be at least three days."
Ms Wilkie said the situation was being managed, but "when something like this happens it's like a domino effect".
"The staff have been working hard today, trying to sort it, but people should expect delays."
The phones are working, but Ms Wilkie said voice messages could not be accessed.
She said the area where the fire started was away from the main hospital building and there was no danger to patients or staff.
The computer issues are also affecting services offered by the child development team, mental health services and the Lakes Needs Assessment Service Co-ordination.
Rotorua Fire Brigade senior station officer Ben Alton said the fire was primarily controlled by the hospital's carbon dioxide drenching system - "a system that uses gassing rather than sprinklers for electrical items".
An investigation into the fire is expected to be completed tonight.
