PECO says an electrical problem may have started a transformer explosion.
The incident occurred around 3:30 p.m. in the 100 block of West Main Street.
Witnesses reported smelling an odor of gas, followed by several underground explosions.
Electricity has been shut off in the 100 and 200 blocks of West Main Street in Norristown. 31 customers are without power.
Three buildings have been evacuated.
There are no reported injuries.