The identities of the shooter and the victims were not immediately available.
A man showed up to Mercy Hospital Monday afternoon and opened fire on a woman believed to be his former fiancee before turning the gun on others, killing four people, including a police officer and the gunman himself.
Chicago police officer Samuel Jimenez died in the line of duty, Anthony Guglielmi, chief communications officer for Chicago police, confirmed on Twitter.
Chicago fire officials told ABC7 that two women were shot between 3 and 3:30 p.m. CT, and one of them - who was hit in the parking lot - was a doctor at Mercy. Her former fiance was the shooter, a source told ABC7. Both of the women were taken to other hospitals nearby.
The identities of the shooter and the victims were not immediately available.
A SWAT team responded to the 292-bed hospital near Interstate 55. Nearby buildings, including the National Teachers Academy, were locked during the attack. Mercy Hospital tweeted later that the incident was over and that all patients were safe.
Lenice Donaldson, a pharmacy technician at Mercy, said she was in the back to get a drink and had just returned as she heard the gunshots. She and the other technicians locked themselves up until police got them out, she said.
"It's just unbelievable. We came out with our hands up, and there was blood all over the floor in the lobby," Donaldson said. "It's a shame."
Tracy Lyons, a cancer survivor, said she goes to Mercy for regular radiation treatments. She described listening to the gun battle between police and the shooter until a SWAT team freed her and some technicians from a lab.
"It was just nothing but pow-pow-pow," she said. "We thought we would never get out of there."
According to the Associated Press, James Gray told ABC7 that he saw multiple people shot: "It looked like he was turning and shooting people at random." In an interview with CBS Chicago, a witness who was in the hospital said she saw blood by an entrance. Another witness said he saw a gunman shoot someone multiple times in a parking lot. He added that officers responded quickly and exchanged gunfire with the shooter.
Sen Dick Durbin, D-Ill., wrote in a Monday evening tweet that he was praying for the victims of the shooting and their families.
Also on Monday, according to the St. Louis Post-Dispatch, police in suburban St. Louis were searching for a gunman who went into a religious supply store, sexually assaulted at least one woman and shot a woman in the head, leaving her in critical condition at a hospital.
The shooting happened about 3:15 p.m. at a Catholic Supply store in western St. Louis County, near the town of Ballwin. Police were searching for the gunman and said he should be considered armed and dangerous.
In Philadelphia, two men and two women were 'executed' in a home, according to ABC. And in Denver's Lower Downtown neighborhood, one person was killed, and at least three others were sent to a hospital after a shooting, according to the Denver Post.
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The Washington Post's Keith McMillan contributed to this report.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)