A "massive fireball" was seen by staff at a Taupo workshop before their welding bay erupted in flames.
Fire crews from Rotorua and Taupo were sent to battle the fire at Dudley Mechanical Preps on Manuka St in Taupo today.
The fire is believed to have started in the shop's welding bay, containing a compressor.
Fire crews were called to the scene about 11am.
Dudley Mechanical Preps staff member Aaron Elmiger said they were all out of the building when the fire started.
"We had just finished smoko when we saw this massive fireball and then it erupted and was all go from there.
"It got too big too quick for us to do anything with fire extinguishers so we didn't know what to do. I guess the next thing for us is to see what the damage is."
He said the roof had partially collapsed and it was lucky nobody had been inside the building at the time.
"The firefighters got it under control pretty quick... I don't think we'll be able to salvage much from that area... We have no idea how it started."
Fire safety investigator Stuart Booten arrived at the scene this afternoon. He said he did not know when he would be able to say what caused the blaze.
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