Dyfed-Powys Police is appealing for witnesses.
It's after a suspected arson at a house at Erw Las, Llanelli, at around 1:20am on Monday, April 24 2017.
The occupants were asleep inside, nobody was harmed.
A 27-year-old man has been arrested on suspicion of arson with intent to endanger life and remains in police custody while investigations continue.
Police are keen to speak to anyone with information that can help them with their enquiries; particularly if you saw someone carrying a fuel can in the area at the time of the fire.
Contact Llanelli Police by calling 101 number, or you can report information anonymously to Crimestoppers on 0800 555 111.