Some people were evacuated from their homes as firefighters tackled a 'large" blaze at an industrial estate at Milford Haven during the night.
Crews were called to Dyfed Cleaning Services on St Peter's Road just before 2300 BST on Wednesday
Mid and West Wales Fire and Rescue Service said the whole building was alight but nobody was thought to be caught inside.
Some firefighters were still at the scene at 0700 BST.
At its height about 40 firefighters from several stations in Pembrokeshire fought the blaze.
The service said the operation had been scaled back but a crew was still monitoring the site.