"I saw it start. I just walked out the door and saw flames coming out the chimney on the right. The flames would have been 20-30ft [6-9m] or maybe higher. And when I ran across you could see the bottom of the bake oven, the front bit, was well and truly burning too," he said.
Mr Robertson alerted a panelbeater spraying in the booth to the flames behind his back.
"It all happened pretty quickly. A guy was actually in there when it happened - as I yelled out he turned and saw the flames behind," he said.
The employee threw a bucket of water on to the blaze, before he and owner Graeme Logan tried unsuccessfully to extinguish it using on-site hoses. Mr Robertson said he helped staff to remove vehicles from the compound and ferried files and computers across the road.
"Everybody was trying to get out and get all the vehicles out.
"I've spoken to [owners] Graeme and Gillian Logan. They are pretty distraught. He [Mr Logan] was pretty shaken. Anytime you get a fire like this, it's pretty devastating," he said.
Dean Henriksen, an employee at Colin Davis Panelbeaters, was in the panelbeating area of the business when he was alerted to the fire. He said there were about eight employees on site and all managed to get out unscathed.
After assisting his colleagues to remove the cars from the workshop, Mr Henriksen went next door and helped Filthy Few members wheel their motorbikes from the headquarters across the road to the Plumbing World carpark.
A Plumbing World employee, who would not be named, was with a customer when she noticed large flames flickering from the top of the panelbeaters.
"The roof was engulfed with orange flames that were coming out of one of the chimneys. ... I called 111 and the fire brigade were here in less than a minute. The wind was ebbing the fire on to the Filthy Few pad and I don't know if their place caught on fire but I suspect the heat was enough to bring them out."
The woman said the flames were a greeny-grey colour and the fire produced "a lot of smoke".
Business owner Ms Logan sat outside the property while firefighters extinguished the blaze. She was "absolutely gutted" but remained positive about the situation - no one was injured, no cars were damaged and they had insurance. The panelbeating area was owned by the business but the painting area, which burnt, was a rental property.
"Business will carry on as usual. We've got to get our heads around this but I'm sure we'll work something out."
Police officers in several cars blocked roads near the fire while about 20 firefighters from Greerton, Tauranga and Mount Maunganui battled the blaze.
Tauranga Fire Service senior station officer Mark Keller confirmed the fire originated in the rear of one of the spraying booths but said firefighters were yet to determine what caused the blaze.
"There is considerable damage, it's pretty extensive in there. I'd say about 30 per cent damage. They won't be able to trade out of there for a wee while yet, there's quite a bit of rebuilding work to be done."
Mr Keller said the Filthy Few premises was not damaged by the fire.