Winpy Byrd, how owns Byrd's Wholesale, Inc., said it was actually his cigarette that caused it.
"I dropped it and the wind picked it up and nobody could see it. We've got pictures where it smothered out and then flames," he said.
The fire broke out Thursday around 7:30 p.m.
Captain Bentley Powell with the Smithfield Fire Department said no one was at the warehouse at the time of the fire.
Johnston County fire crews battle large blaze at Byrd's Wholesale, Inc.
He also mentioned the building contained wood products and a mill inside where lumber was sawed.
The owner said he's been at that property since 1969.
Crews were on scene throughout the night to monitor hotspots.
Firefighters said the wind was working against them and reigniting the hotspots.