The boy's mother drove the child to the hospital, where he was treated for injuries that were not life-threatening, police spokesman Officer Albie Esparza said.
The boy was hit after getting out of a parked car at Capitol Avenue and Lobos Street at about 6:50 p.m., according to Esparza.
Esparza said the boy's mother witnessed the crash from across the street and called police. A friend of the mother was also getting out of the parked car at the time.
The boy had apparently exited the driver's side and was standing near the front of the vehicle when he was hit by a burgundy, 1980s-model four-door Honda driving south on Capitol Avenue, Esparza said.
The boy's mother told police she heard a "boom" and saw her child lying in the roadway, according to Esparza.
The woman said she saw the driver of the Honda, a Hispanic man of unknown age, stop, get out and ask, "What happened?" then drive off, Esparza said.
Anyone with information about the case is asked to contact the Police Department's hit-and-run detail at (415) 553-1641. Those wishing to remain anonymous can call (415) 575-4444 or text TIP411.