Neighbors say they heard what sounded like an explosion at about 1:00 a.m. on Monday, just before flames burst from the front and back of the two houses in the unit block of West Clinton Street in Clayton.
Everyone in the homes managed to get out safely.
The fire department responded quickly, and firefighters were able to put out the flames in a matter of minutes.
The fire marshall is now trying to determine exactly what sparked the blaze.
