The 2-inch plastic main ruptured at about 5:40 a.m. at Mission and Randall streets, said Tyrone Jue, spokesman for the San Francisco Public Utilities Commission.
Crews today were repairing the pipe, which is made of an older plastic material, SFPUC spokeswoman Suzanne Gautier said. She said the agency no longer installs plastic pipes, but that this pipe will be fixed rather than replaced.
Gautier said the leak has been stopped and there was no interruption to water service. She could not say how much water leaked.
Don Nugent, a manager at Don's Auto Service, said that as of about 8:30 a.m., water was running down the street, but that it looked like crews had almost finished stopping the leak.
He said repair crews blocked at least one lane on Mission Street while they worked.