The incident began at 1:18 p.m. when a construction crew hit a gas line, sparking an explosion and fire at Geary Boulevard and Parker Avenue.
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The eight to 10 crew members on the scene were safely evacuated and no one was hurt.
VIDEO: Audio captures terror after SF gas explosion
At least five buildings, including the Hong Kong Lounge II restaurant, caught fire.
The fire department ordered the evacuation of a one-square block area, while PG&E crews worked to shut off the gas.
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"It's complicated what they have to do, get into the street and shut that down, while keeping their workers safe, it's really a third alarm, that's what it is at this point," said SF Fire Chief Joanne Hayes White.
VIDEO: Huge flames seen from gas explosion in SF
A third alarm response means more than 100 firefighters are on the scene.
It took about two hours and 20 minutes to turn off the gas and then fire went out.
Take a look at full coverage on the gas explosion and fire on Geary Boulevard in San Francisco.