The blaze consumed five buildings at Geary Blvd and Parker Ave Wednesday afternoon.
Hayes-White says the leak happened while an underground construction crew was working in the area.
RELATED: San Francisco crews respond to fire possibly sparked by gas explosion near USF
According to PG&E officials, 300 customers are without gas and 2,500 are without electricity.
Crews are working to restore both gas and power but said it is a "complex web of utilities" and they're going slow and methodically.
Take a look at full coverage on the gas explosion and fire on Geary Boulevard in San Francisco.
VIDEO: SKY7 footage over massive fire sparked by gas explosion in SF