Four police officers were shot on Saturday night and early Sunday morning in two separate violent incidents in Chicago and St. Louis. One police officer is in critical condition following a shooting.

At around 6 p.m. on Saturday, St. Louis police officers responded to a gunman who barricaded himself in a home in the Tower Grove South neighborhood. The suspect allegedly started firing at two police officers.

One cop was shot in his leg, and suffered a non-life-threatening wound. The other police officer was shot in the head and "very critically" wounded, St. Louis Police Department Chief John Hayden Jr. told reporters.

"As our brave officers were trying to get him secured, other officers responded to the scene, and another one of our officers was shot in the leg," Hayden said. "Both are at area hospitals. Doctors are working feverishly to assist them."

"While they're on the scene, they hear shots, and our first officer, who is very critically injured, and when I say very critically injured, he's very critically injured, he was shot. He has a head wound. And that officer is down," Hayden said.

The St. Louis Police said the officer is "fighting for his life."

Hayden said both of the injured officers are about 29-years-old, and the critically wounded cop has been on the force for approximately three years.

The suspect was taken into custody after nearly 12 hours, and witnesses say up to 100 police and SWAT officers were involved.

Hayden said there have been eight police officers shot in the line of duty since June 1.

"Our officers have been going through a lot this summer, as you know. We've had a surge in violence," Hayden said. "These officers, all they're trying to do is do their job and help a person that's wounded, and they come under gunfire themselves."

Early Sunday morning, two Chicago police officers were shot during a traffic stop. At 2:33 a.m., police officers were conducting a traffic stop of a "vehicle matching the description from a person with a gun call," according to officials.

Police allegedly spotted a handgun next to a person in the backseat of the car. The cops instructed the person to get out of the vehicle, but he refused to comply.

The officers shattered the vehicle's window to remove the man from the car. The suspect allegedly fired multiple shots at the police and struck both cops. A third officer shot back and hit the suspect.

One officer suffered multiple gunshot wounds to the chest, side and back, according to Chicago Police Department Supt. David Brown. He was transported to John H. Stroger Jr. Hospital in serious condition. The officer underwent surgery for his injuries.

The other cop was shot in the shoulder and chest and transported to the same hospital. He is reportedly in good condition.

The supervisor of the downed cops drove them to the hospital in a police vehicle.

"The quick response and thinking of their supervisors, their sergeant, likely saved precious time for their treatment," Brown said. "That really is important when you have bleeding, gunshot wounds. That time is critical to get the treatment started."

Brown said the wounded cops, who are in their early 20s and have been on the force for about two years, are members of a "summer mobile citywide team recently formed to address violent crime."

The suspect is in critical condition, but has been stabilized.

"When officers leave home, they never really know what the day holds, whether or not they'll be asked to make the ultimate sacrifice," Brown said.

CPD spokesman Tom Ahern posted a photo of the gun that was used to shoot the police.