Officials with the utility company, UGI, said they found no signs of a gas leak but additional tests were still pending.
Neighbors reported hearing a large blast, along the 700 block of Fountain Street, around 3 a.m. but authorities are not calling it an explosion.
Roughly 47 people, including 13 families, were displaced by the blaze.
Demolition crews are now working to tear down the 10 row homes damaged by fire.
Investigators hope to determine a cause soon.