Transcript for Gas line rupture believed to be cause of San Francisco blast
And we're going to begin with the unfolding scene in San Francisco at this hour. A gas explosion sparking a massive fire there. More than 100 firefighters are on the scene, flames shooting dozens of feet into the air. This all playing out on busy Gary boulevard. Gas pouring out from a punctured line. Firefighters dousing the buildings. There have been evacuations tonight, and people are being told to stay away. ABC's will Carr leads us off. Reporter: Just after 1:00 P.M., a fire ball exploding in one of the busiest sections of San Francisco. It was a close call. I feel very lucky to be alive. Reporter: Watch the relentless flames shoot at least 35 feet into the air. Put the water on the building. Copy that. We have fire on the top floor. Reporter: The intense fire fueled by a breached gas line near a construction site where workers were installing fiber optic equipment underground. The explosion rocking the city's inner Richmond neighborhood, during a busy lunch hour, sending plumes of smoke billowing into the sky. Witnesses say a local restaurant was one of four buildings immediately engulfed in flames. Fire crews raced to the scene, more than 100 firefighters attacking the three-alarm blaze for more than an hour. We're trying to get some water. We're not going to extinguish the main. Reporter: With the fire raging, crews et up a one-block perimeter. Neby residents instantly asked to avoid the area for their own safety. We need patience until gas leak gets out. But I'm confident that it will be contained soon. Reporter: Patience, as they try to shut off the gas and extinguish the fire. Let's get to will Carr tonight. And we know this is still unfolding, but despite the images, no words of any injuries tonight? Reporter: That's right, David. There were eight construction workers in the area when the fire exploded. Amazingly, none were hurt. And this is a terrifying scene, according to witnesses. They described those fierce flames and the gas that was rippling throughout the air. Crews now are trying to shut off that gas line as quickly and as safely as possible. David? All right, will Carr leading us off.
This transcript has been automatically generated and may not be 100% accurate.