Fire investigators have narrowed down where Monday's blaze in Hamilton started, but just exactly what caused it remains unclear.

Mushroom clouds of black smoke could be seen from as far as Raglan early Monday as the fire ripped through AH Franks Tyres on Anglesea St - the second suspicious fire at the business in 24 hours, and the third since 2012.

The fire took nearly two days to fully extinguish due to firefighters not being able to access certain areas because of the unstable and fire-damaged southern wall.

Asbestos removal workers at AH Franks Tyres on Tuesday. The worker on the right stands next to where Sunday's arson occurred, which is also near where Monday's fire started. Photo / Belinda Feek
Asbestos removal workers at AH Franks Tyres on Tuesday. The worker on the right stands next to where Sunday's arson occurred, which is also near where Monday's fire started. Photo / Belinda Feek

Large amounts of asbestos left around the scene also had to be removed before investigators got inside yesterday.

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Waikato senior fire risk management officer Kevin Holmes said while the wall was safe enough initially, it was being checked daily for any movement.

"Everyday we've got to make sure that nothing has changed as far as the structure of the wall; has it moved?"

A two-tonne digger was brought in yesterday to help clear the area where the fire appeared to have started - near the scene of Sunday's suspicious blaze where a pile of tyres were set alight against an outside wall.

Due to the vibrations from the digger they did believe the wall moved a bit yesterday so would be re-assessing it again before beginning work today.

The digger was brought in to help clear the target area because of the large amount of debris from not only what was on ground level but also on a mezzanine floor which was used for storage.

The charred remains of AH Franks Tyres. Photo / Belinda Feek
The charred remains of AH Franks Tyres. Photo / Belinda Feek

"The mere size of the incident, this is just the amount of time that it takes. There's just so much you have to look at and consider. You have to look at everything, you have to eliminate everything - it's just painstakingly slow.

"You can't leave any stone unturned."

An electrical engineer arrived yesterday while an insurance investigator was also at the scene.

Seven AH Franks employees now face an uncertain future while owner Jim Nolen is left with a pile of ashes and charred vehicles that he was working on.