At approximately 12:30 p.m., the Millbrae Fire Department called the school notifying them of a nearby gas leak.
"We were told that the leak was just around the corner and were instructed to stay put until they call again," a woman answering the phone at Spring Valley Elementary School said.
The school, located just northwest of the leak on Pinon Avenue, complied and students and staff sheltered in place within minutes, she said.
As of 1:48 p.m., authorities had called to assure school officials that all was clear, and classes had returned to normal.
PG&E spokesman Matt Nauman said the gas leak interrupted service to a home at 815 Pinon Ave.
"It seems as if some city crews out here working on Pinon (Avenue) hit a service line," Nauman said. "It only affected one customer."
A service line is a three-quarter-inch pipe that delivers gas to individual homes, according to Nauman.
PG&E technicians have been called to the scene, Nauman said.
"We've got a hole in the street here and are looking to get this wrapped up as soon as we can," he said.