Investigators say finding the cause of the blaze will be difficult.
They are still waiting to gain access to the building due to the roof collapse, the fire service says.
Ten fire crews tackled Thursday's fire at the 200,000 sq ft (18,580 sq m) warehouse on the Blackpole East Industrial Estate in Worcester.
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Keith Chance, the Area Commander for Herefordshire and Worcestershire Fire and Rescue, said they have some good eyewitness accounts from the members of staff at the delivery company Arrow XL.
"The fire developed very quickly, a large proportion of the roof collapsed into the building so gaining access to identify exactly what happened will be difficult."
Ian Howell, the chief executive of ArrowXL said they are committed to keeping their business local to the area.
"We have been in the area for the best part of 25 years and we're committed to staying in the local area and have no plans to move away.
"We've just got to work through where we are, it's a bit too early to tell but clearly there's a big job in terms of rebuilding the site."
"The only thing that really matters is there's been no loss of life whatsoever, stock can be replaced, operations can be resumed."
The fire service says it will keep a presence at the warehouse for the next few days to make sure no hot spots in the building flare up.
A "major" fire at a warehouse has badly damaged the building, causing most of the roof to collapse.