The emergency services were also at the scene and one woman has been taken to hospital.
The fire service received a call at 8.07am and crews from Milford Haven, Haverfordwest and Pembroke Dock were sent to tackle the blaze.
Mid and west Wales fire service said it was believed the incident had been caused by gas and residents were evacuated from the surrounding area.
The fire was said to be under control by 11am but crews remained at the scene damping down.
The fire service said the woman, believed to be elderly, who lived at the property had not suffered life-threatening injuries but was in shock.
Residents said an explosion at the house blew out a window but the female occupant was able to walk out before being taken to hospital.