Crews have now put out the fire at Environcom's building in Rufford Street in Lye, Stourbridge, after being called just after 7.30am.
The company has since revealed the "severe" fire was caused by a fault with a fridge which burst into flames during routine testing works - but investigations remain ongoing.
Firefighters were at the scene within five minutes and fought to extinguish the flames after all people inside the building managed to escape.
West Midlands Fire Service crews are expected to remain at the site for most of the day.
WATCH: How the blaze was tackled
Amazing, assertive work by our firefighters means the large fire in Rufford Street, Lye is now out and we'll soon be scaling down our resources at the scene. However, we'll have some crews there for most of the day and nearby roads will be closed for a couple more hours. pic.twitter.com/4EtKJ6efUv— West Midlands Fire Service (@WestMidsFire) August 1, 2019
Incident Commander Lee Baker said: "Crews have done a remarkable job containing the fire in a group of white goods in a factory building.
"The fire has been contained and put out.
"Crews will be here most of the day dampening down and assisting with the investigation, and supporting the business in getting back into use."
GALLERY: Crews battle the blaze in Lye
Firefighters were deployed in 10 engines and used an aerial platform to battle the blaze.
Water, gas and electrical engineers were also on site, with damage contained within the building which contains plastic goods and recycled items.
'Fire spread from tested fridge'
Jon Parsons, Environcom finance director, confirmed the flames spread after one fridge caught fire as staff were carrying out function tests.
He added: “In our re-use department, where we’re carrying out function testing of electrical appliances prior to re-use, a fire has occurred on a fridge that was on function test.
“That fire spread to adjacent fridges but was quickly identified and contained by firefighters.
“All electrical appliances that go through our re-use area undergo a 32-point test, to make sure what we’re selling is electrically safe as well as working."
Mr Parsons added: “We’re regulated by the Environment Agency, which gives everybody confidence that through our testing process we’ll try and identify as many potential faults as possible.
“So we’re very thankful that when this appliance caught fire, it was within our factory where we’re trained and capable of dealing with it far better than it occurring in somebody’s home.
“I understand the fire is limited to our re-use area, which is a very manual area, so we don’t believe there is any structural damage to the building, and hopefully we’ll be back up and running within a few days.
“We like to thank the fire service for their quick response and for keeping the fire contained to this small area.”
'Serious incident avoided'
Gas and power to the site was isolated when crews arrived at the brick and steel clad building, which is 90 x 60 metres.
Rich Stanton, West Midlands Fire Service group commander, said: “We mobilised a number of crews and at the height of the incident we had 10 fire engines and one of our hydraulic platforms.
“There’s been no casualties or injuries reported at this incident and our teams have done an incredible job.
“This could have been a really serious incident with a railway line nearby but our crews acted quickly and contained the fire to a small section, and bringing it under control.
“Crews will be on scene for most of the day to dampen down and make it safe.
“The cause of the fire is not known and crews are investigating.”
Stourbridge Road was closed by police near to the train line heading to Lye railway station and was reopen by 1pm.
Bus services have also been affected, with National Express West Midlands confirming it has diverted its number 9 service.
Drivers are still being diverted along Cemetery Road while Stourbridge Road remains closed.
Our reporter Liam Keen at the scene
It’s just been confirmed to me that firefighters are “scaling down” the incident, meaning many of the firefighters are being relieved, with day officers replacing those that have been here since 7.30.— Liam Keen (@LiamKeen_Star) August 1, 2019