Bloody Burgers owner Kamal Khetpal said he was not working at the time of the fire but he had experienced staff members on duty.
“One of the guys was changing the oil and he’s very experienced, but he forgot to turn the switch off of the fryer before the draining of the oil.
“There was still some oil left in the fryer when he went outside to empty it.”
The fryer element began overheating and caught fire.
Another staff member saw a fire had started and switched off the fryer before grabbing a fire extinguisher but was unable to completely put out the fire.
“It was still sparking.”
Khetpal said he was sorry for the inconvenience and loss of trade it had caused for other stores in Trafalgar Square which had to be evacuated.
“I hope this helps other businesses and people to remember to take precaution, we did have a note there ... but when people get used to it they sometimes just ignore it.”
The fryer was broken and Bloody Burgers would have to remain closed for a short time while an insurance company assessed the extent of the damage.
“Obviously we’re going to be closed but mentally it will affect people as they may be worried about working in the store for a little while.
“But it’s an accident and it could happen with anybody, the guy who was changing the oil has done that job probably 50 times before.”
Khetpal said he was glad nobody was hurt or injured: “That’s the main thing.”
Fire crews left the scene about 10pm.
Eva de Jong is a reporter for the Whanganui Chronicle covering health stories and general news. She began as a reporter in 2023.