A decision on when to reopen McDonald's in Victoria Ave will be made today.
The city centre restaurant is closed after a fire in the kitchen on Wednesday night.
McDonald's spokesman Simon Kenny said the fire started in a vat unit just after 6pm.
"People might hear that it was a vat fire and assume the oil caught fire, but that wasn't how it happened," he said.
"It was an electrical fire in the vat unit itself, we believe."
The cause of the fire is still being investigated.
As soon as the fire was discovered, staff sounded the alarm and evacuated all customers from the restaurant.
"There were no injuries apart from a minor injury to a staff member, sustained when he broke the glass to turn the alarm on," Mr Kenny said.
The restaurant filled with smoke and the fire service was called to put the fire out.
Part of Victoria Ave was cordoned off by police while the firefighters dealt with the fire, and traffic was diverted.
Mr Kenny said damage to the restaurant was restricted to an area of the kitchen.
"Fortunately, the fire was isolated to just the vat unit and the ceiling above.
"Right now it's a matter of cleaning the restaurant up and getting rid of the smoky smell."
He said the vat unit would not be used again, and a decision on whether a replacement was needed would be made today.
The restaurant would not re-open until that decision had been made.