Unexploded gas cylinders are concerning firefighters at a blaze at a Tauranga auto-electrical workshop this morning.

It took firefighters more than an hour to put out the blaze that engulfed the two-storey building before dawn.

Fire and Emergency spokesman Daniel Nicholson said the cylinders were filled with argon and were "being treated with caution".

A fire safety investigator was also at the property to determine how the blaze started.

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Earlier Fire and Emergency Northern communications shift manager Megan Ruru said six crews were at the fire that had engulfed the two-storey property in the suburb of Judea.

She said the alarm was raised at 4.40am.

The Koromiko St property was burning fiercely when firefighters arrived, she said.