Firefighters were called to the building fire at RIP Car Wreckers on Valley Rd at about 11am. Six crews attended and extinguished the blaze, a Fire and Emergency NZ spokesman said.
He said the building measuring 40m by 20m was earlier engulfed.
There were no injuries, and a fire investigator had been on-site to determine the cause.
The couple had owned the business since December 2019. She said although they were both reeling - "these things happen".
When asked what the next few days might look like for the pair, she said they would get up tomorrow and begin to deal with what was left.
"Let's hope it's better than today."
Rackham said she was not able to say whether anyone had been inside at the time of the fire or speculate the cause as a thorough fire investigation was underway.
A police media spokeswoman said they were called to help with traffic control and diversions were put in place at the intersection of Alexander and Valley Rds, and Gorge Rd and Commerce St.
Whakatāne resident Judy Doyle was on her way home from her weekly exercise class and saw the smoke as she turned onto Valley Rd.
Driving towards the blaze, she said she could feel the heat from inside her car, and got out to watch crews battle the fire.
She said she could hear gas cylinder explosions and by the time she left, the building was starting to collapse. She said one side of the building had old cars and she was unsure whether or not they would catch alight.
Rochelle Beale lives around the corner from the industrial side of town and said she smelt burning tyres before she knew there was a fire.
She said she could see "thick, black smoke" and "the top of the flames flicking up ... just the colour red" from her two-story house.