An electrical fault was the cause of a fire at a Warrnambool business property on Wednesday.

Warrnambool CFA station officer Lachlan Ross said no one was harmed in the incident.

"There's two business in there and both the owners and one of the owner's sons were all at work at the time and were able to evacuate with no injuries or adverse effects."

Mr Ross said crews monitored carbon monoxide levels and worked to ventilate the property in the afternoon before officers could enter.

"It was pretty difficult to ventilate because of the structure and how it was built with a lack of windows," Mr Ross said. 

"We got it to a stage where we could go in with our breathing apparatuses. Myself and Vic Pol went in and we were able to ascertain it was an electrical fault from an exhaust fan."

He said two businesses operated from the premises including Designers by Nature and Regional Health Plus. Ocean View Photography, which still has signage at the property, is no longer based at the premises.

Mr Ross said it was a timely reminder for home and business owners to have working smoke detectors at their properties.

Earlier: 2.15pm Wednesday

Police and CFA officers are on the scene of a building fire at the rear of a Liebig Street business. 

Warrnambool CFA station officer Lachlan Ross said they were called to the rear of the premises of Ocean View Photography at 12.40pm to reports of smoke coming from the bathroom.

Four trucks from Warrnambool responded to the fire, which they battled from the Ozone Carpark. 

"We arrived on scene with smoke exiting the rear window attached to the bathroom and toilet," Mr Ross said.

"We sent crews inside, they conducted an aggressive attack and were able to contain the fire to that area and now it's clearing smoke out so we can get people in without getting sick." 

Mr Ross said officers were yet to determine the cause and the first priority was to dispel the smoke so they could get CFA officers inside to investigate how the fire started.

He said CFA crews used water to draw smoke from the building.

"We've been trying to force it out but because these old buildings are so compartmentalised they lock down and it's really hard to get smoke out of them so it's a different method," he said. 

Powercor staff were also on scene waiting for smoke to clear so they could gain access and cut the power.

Powercor linesman Matt Riordan said once they were allowed inside they would need to locate the power supply for the two businesses inside the premises, without cutting access to nearby shops.

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