The fire service say investigators will be arriving at the scene of this morning's blaze at Blackwood's Pound Stretcher store shortly to begin an investigation into the blaze.
Crews will spend the rest of the day dampening down the building say officers.
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Fire crews have been responding to reports of flash flooding in Carmarthenshire. Some homes have been affected.
Medication designed for animals was taken from the building in Abertillery on Thursday night.
More than a thousand riders will be taking part in a series of events in and around the town.