Police officials say officers were called to the facility around 3:30 p.m.
Arriving officers found two gunshot victims. Their conditions have not been released.
Law enforcement officials tell ABC News that preliminary information indicates the incident began when one hospital employee shot two other employees.
The alleged shooter may have been only a temporary employee. The suspect's identity is known to police, who are currently conducting a manhunt.
The conditions of the injured are not known at the moment.
Police believe the incident is strictly a workplace shooting, ABC News has learned, though officials say the scene is still active and the info could still change.
Brian Pfeffer is a hospital guide who was in the Emergency Department at the time. He said he heard the shots, and was there as armed police entered the building.
"It was super intense. I'm kind of shaking," he said. "God forbid anyone should have to be a part of that."
Chopper 6 video from 6abc Action News in Philadelphia showed people leaving the hospital with their hands up.
Video showed a number of police vehicles at the entrance to the hospital's Emergency Department late Tuesday afternoon.
A large number of police, firefighters and medics could be seen from Chopper 6.
The hospital is in lockdown, and Wilmington police are asking the public to avoid the area.
This is a Developing Story. Please check back for updates.