It happened just before 2:30 p.m. at the 24/7 Pet Vet Clinic off of Fresno Street and Peralta Way. The fire department responded with a hazmat team, safely evacuating everyone inside the building -- including the animals.
A female customer, along with another person, was transported to the hospital. Four employees inside the building were treated at the scene, while some people complained of breathing problems.
Pets are were held at the building across the street.
It is unclear where the odor originated. Officials are investigating to determine the substance.