A Chicago police officer is fighting for his life after being shot early Wednesday morning.

The 25-year-old off-duty officer -- who has not yet been identified -- was driving past an elementary school in the city's South Side just before 2 a.m. when someone in a black Toyota fired about 20 shots, striking him in the head with at least one, police say.

"I first want to ask you all for your prayers for this officer, who has been a Chicago police officer for just two years," Chicago Police Department Superintendent Eddie Johnson said Wednesday during a press conference.

After being hit, the officer was taken to the University of Chicago Medical Center where he went into emergency surgery but remains in critical condition, police added. Johnson said detectives are still investigating the shooting and asked anyone with information to come forward.

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Chicago Fraternal Order of Police President Kevin Graham said the officer was showing signs of improvement. Johnson mentioned he was responding to stimuli and gave a thumbs-up from his hospital bed.

The officer was driving with a female companion when they realized the black Toyota was following them, police said. The woman called 911, and seconds later, the shots were fired. She was not injured. Officers who were conducting a traffic stop nearby responded to the scene after hearing the gunfire.

Johnson said other members of the officer's unit visited him in the hospital overnight. He, in his remarks, also decried the rampant gun violence in Chicago.

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"You ask yourself 'Why does this keep occurring?' and the simple fact is we just have too many guns in Chicago and too many people willing to use them," he said.

He also called for his city to "put the guns down."

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"I also want to offer a prayer to all those who have suffered as a result of gun violence in Chicago," Johnson said. "These senseless shootings just have to stop, and I'd like to renew my call for common-sense gun laws, I'm also calling for a renewed sense of humanity -- we need to put the guns down in the city of Chicago."

Chicago saw 561 homicides in 2018, which is down from the two previous years.

Fox News' Tyler Olson contributed to this report.