Chicago hospital shooting leaves four dead

A gunman shot to death a doctor outside the Mercy Hospital in Chicago on Monday before bursting into the facility and killing a woman and a police officer during an exchange of gunfire and dying in the shooting, officials said.

The shooter knew the doctor he shot outside Mercy Hospital, but once inside he fired randomly at people, Chicago Police Superintendent Eddie Johnson said at a news conference.

The shooting sent doctors and patients streaming out of the facility, some with their hands up as heavily armed police officers sought to secure the facility.

"The city of Chicago lost a doctor, a pharmaceutical assistant and a police officer, all going about their day, all doing what they love," Chicago Mayor Rahm Emanuel told reporters.

"This tears at the soul of our city. It is the face and consequence of evil," Emanuel said.

The police officer, Samuel Jimenez, died in an exchange of fire with the gunman after he entered the medical facility, Johnson said.

The gunman, whose name has not been released, also died, officials said. But it was not immediately clear if he shot himself or if he was struck by a police officer's bullet, Johnson said.

Another officer was spared injury when a bullet lodged itself in his holster, Johnson said.

One witness named by the local CBS television affiliate as Hector Avitia said he was with his wife waiting for test results when he saw a gunman dressed in black fire on someone on the ground multiple times in the parking lot.

He said the gunman was carrying a handgun with multiple clips.

"Then almost immediately, an officer was already coming in an SUV and he exchanged fire at them and then reloaded and shot the person on the ground again and then he made his way into the hospital and more shots were fired," another witness recalled.

Mercy, founded in 1852, has locations throughout Chicago and provides outpatient treatment and acute inpatient care, boasting doctors who are leaders in their field.

In Denver, another shooting left one person dead and three others wounded on Monday. At least one suspect remained at large after the shooting on a downtown street corner. 

The shootings followed a series of recent high-profile gun rampages that have fueled calls for reform of firearms regulations in a country plagued by gun violence.

Less than two weeks earlier a gunman killed 12 people in a California music bar packed with college students.

That came after the worst anti-Semitic attack in modern US history, when a gunman opened fire on worshipers at a synagogue in the US city of Pittsburgh on October 27.