By about 12:30 p.m. ET, local authorities had evacuated or sheltered in place just over 240 homes.
The gas main broke in the area of Scenery Drive and Brandermill Drive near Captain James Daley Elementary School in Germantown.
A third party had been drilling in the area before the break occurred.
Montgomery County fire officials are currently on the scene trying to contain the leak.
Homes are being evacuated on Brandermill Drive from Scenery Drive to Route 355.