The crash was reported at about 7:55 a.m. at Geary Boulevard and Spruce Street.
The ambulance was responding to a medical call and was traveling east on Geary Boulevard with its sirens on when it was hit by a vehicle traveling north on Spruce Street, fire spokeswoman Mindy Talmadge said.
The paramedic, who was on the passenger side of the ambulance, was taken to a hospital to be evaluated.
Two people in the other vehicle were also hospitalized, Talmadge said. She did not know the extent of the victims' injuries.