The Chicago Police Department warned of a "heavy police response" coming to the area following "reports of shots fired." At least "one possible offender" had been shot, police said. Less than six people were wounded in total, a law enforcement source told the Chicago Tribune. However, that number has been updated to six if the gunman is included.
The officer that was shot is "in critical condition but receiving excellent care," Chicago Police Department Chief Communications Officer Anthony Guglielmi tweeted.
The gunman's motive remains unknown. He is believed to have used a pistol, local media reports.
Shots reportedly rang out from both inside and outside of the hospital, which was evacuated. A heavy police presence responded to the scene and at least 15 ambulances were dispatched.
Witnesses that spoke to ABC 7 Chicago report hearing anywhere from six to nine gunshots.