A policewoman has been shot and killed unintentionally by a fellow officer.

Krystal Rivera, a 36-year-old officer with the Chicago Police Department, Illinois, was shot and killed in the line of duty on Thursday evening in the city’s East Chatham neighbourhood.

The events began about 9.50 pm in the 8200 block of South Drexel, as officers on patrol with the 6th District Tactical Team attempted to make an “investigatory stop” of a suspect believed to be armed.

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The suspect then fled on foot into a nearby apartment as police chased behind, said Chicago Police Department Supt. Larry Snelling.

When officers arrived at the apartment, they were confronted by another person inside, who pointed a rifle at officers.

At some point during the encounter, an officer discharged his weapon, Snelling said.

Rivera was struck by gunfire during the confrontation, Snelling said, with officers transporting her to a nearby hospital.

As they were en route, the police vehicle reportedly malfunctioned and caught fire, Snelling said. Rivera was then transferred to another car.

The officer was pronounced dead at the hospital, police said.

About 3am, dozens of police officers and firefighters lined city streets as a procession took place from the hospital to the Cook County Medical Examiners Office.

In a social media post, Pastor Donovan Price said he spent the evening praying with officers at the University of Chicago Medical Centre.

According to Snelling, two people inside the apartment fled the scene, but were taken into custody a short time later.

Snelling added that police have “several individuals in custody”, including one who police believe was on scene when officers were confronted inside the apartment.

Three weapons were recovered from the scene, Snelling said, but it wasn’t immediately clear how many armed suspects there were, or how many people fired weapons.

Police and the Chicago Office of Police Accountability, which responds anytime an officer fires their weapon, were both investigating the circumstances surrounding the incident.

“She had already processed two other guns working that day, “ Snelling said.

“She was a working police officer trying to keep the street safe. And she did great work. And if you talk to anyone on her team, they would tell you how great of a worker she was. This is the risk that our officers take every single day.”

“I want everyone to understand one thing,” Snelling said.

“Our officer that we lost tonight, this happens way too often. An officer, a young officer, 36-years-old and four years on the job. Who was working hard...these officers are out here driving down crime while putting their lives at risk.

“I want everyone to keep this officer’s family in your prayers and understand the risk that she took every single day when she came out to do her job.”

Snelling added that police were issuing a search warrant for the apartment, and the investigation was in its preliminary stages.

“We are we’re not going to release any information until we have all of the evidence and we can really decipher what occurred at that scene,” Snelling said.

Later Friday morning, evidence technicians could be seen walking in and out of the apartment, carrying boxes and bags, with police cars parked outside.

The Chicago Police Department has released the official photo of Krystal Rivera, hailing the 36-year-old mother and Irving Park resident as a “courageous and compassionate officer who devoted her career to helping others and protecting our city”.

During a news conference overnight, Snelling said Rivera was a four-year veteran of the force, and the mother of a young daughter.

“She was a mom, and there’s nothing like walking into a room and having to deliver this type of message to her mother and her very young daughter and the rest of her family,” Snelling said during the press conference.

“No matter how old your children are, they’re still always your children, and for a mother to lose her daughter like that knowing that she was trying to do the right thing every single day, that she was protecting lives, that she was a hero, and she lost her life tragically doing the job that she loved.

“That was one of the things that her mother said, she loved her job, and the way that she worked.”

In an Instagram post, the Chicago Fire Department posted a picture of Rivera, saying she “made the ultimate sacrifice in service” to the city.