An "explosion" caused houses to shake and fill with smoke after a fire broke out near an industrial estate.
Emergency services responded to reports of a fire in a commercial property in Nevills Dock, Llanelli, at about 10.30pm on Monday.
Residents living nearby reported hearing a "loud bang" before their home filled with smoke.
Dyfed-Powys Police said they are investigating the incident but no-one is thought to have been injured.
Mid and West Wales Fire and Rescue Service said two crews left the scene at about 1am on Tuesday morning.
Sarann Williams, 30, who lives on the adjoining New Dock Road, said: "We were watching TV and heard this explosion and the whole house shook then the house was just full of smoke and a really nasty smell so we left to get fresh air and we went around the corner to see what it was.
"The flames were huge. The photos don’t do it justice. Loads of fire brigades and police in the area tackling it.
"We rang 101 to see if the fumes in the house were toxic or not because it was so bad but they said it was nothing to worry about and they were looking into an incident."
A number of other residents reported the loud bang around 11pm on Monday night and saw smoke near the area.
Dyfed-Powys Police said they attended the scene and are investigating the fire.
A spokesperson for Dyfed-Powys Police said: "We can confirm we are investigating a fire at a commercial property in Nevills Dock, Llanelli, on the evening of March 9.
"We were called at approx 11pm but fire service were already in attendance. Thankfully no-one injured as far as I am aware."
Mid and West Wales Fire Service said: "On Monday 9th March at approximately 22:22, crews from Llanelli Fire Station and Tumble Fire Station attended an incident at Copperworks Road, Llanelli.
"Crews used five breathing apparatus, two hose reel foam jets, one main foam jet and two thermal imaging cameras to extinguish the fire.
"Crews left the scene at 01:05am (10th March)."
