The incident was reported at 11:38 a.m. today at the hospital, located at 900 Hyde St. between Pine and Bush streets.
A post office near the hospital, at 1400 Pine Street, has been closed. Two employees were taken to the hospital.
Fire spokeswoman Mindy Talmadge said crews are "testing a substance on somebody's clothing" at the hospital.
No other information about the incident was immediately available.
Stay with ABC7 News for the latest details on this developing story.
(ABC7 News contributed to this report)