A HAZMAT team responded to Sharp-Rees Stealey Medical Center located at 10234 Genetic Center Dr. on Tuesday morning.
The incident happened around 9:30 a.m. when a person at the facility said they felt sick. More people reported a similar illness, forcing 100 people to evacuate from the building.
Seven people were transported to the hospital for symptoms of nausea and dizziness, according to the fire department.
HAZMAT determined the cause of the incident to be an overheated air conditioning belt. Fire officials and HAZMAT have reopened the building for the remainder of the day.
Officials at Sharp said Urgent Care remained open during the evacuation.
The medical center is located on Genetic Center Drive, north of Mira Mesa Boulevard in Sorrento Mesa and just west of Camino Santa Fe.