A Chicago police officer assigned to bike patrol in the Central District was shot and a suspect was killed in an exchange of gunfire with a man who had reportedly been “acting erratically” at a park Thursday evening in the Prairie District neighborhood, authorities said.

One officer was taken by fellow officers to Northwestern Memorial Hospital from the shooting scene at Battle of Fort Dearborn Park after suffering what Chicago Police Superintendent Eddie Johnson said were non-life-threatening injuries. The other man was killed in the shooting a little after 8 p.m. Thursday, Johnson said.

The officer was expected to recover after being shot in the leg, sources said.

Johnson, outside Northwestern Memorial, said that bicycle officers were told by a citizen that someone was “acting erratically” in the park. Officers went to where he was in the park, where they found him on his cell phone.

The officers asked him to get off the cell phone to talk to them, but instead he reached into a backpack and started firing at them. The officers returned fire, hitting the man, Johnson said.

The injured officer was able to apply a tourniquet to his own leg with the help of his partner, probably saving his life, Johnson said. The officer had received training in emergency medical treatment, Johnson said.

The man shot also was taken to Northwestern Memorial Hospital. Information was not immediately available about whether he was pronounced dead on the scene or at the hospital.

The officer who was wounded is a 17-year veteran of the force who is assigned to bike patrol in the Central District, Johnson said. Mayor Emanuel visited the officer in the hospital, Johnson said.

“People like to second-guess, but these officers have a split second to decide whether to use deadly force,” Johnson said.

Emanuel released a statement after the shooting, saying the officer is “an example the courageous and selfless men and women in the Chicago Police Department who do difficult and dangerous work every day, often with little fanfare.”

“Amy and I are hopeful for a full and speedy recovery, and our thoughts are with the officer’s family, friends, and his fellow brave men and women in uniform,” the statement continued.

At the scene, several squad cars, marked and unmarked, sat in the street near the park, which was cordoned off in yellow tape. The area of 18th Street and Calumet Avenue in the historic Prairie Avenue District is dotted with townhomes and some high-rises.

A Chicago police command van sat at 18th and Calumet, where a police-issued light truck also sat, shining a white beam onto the a grassy area of the park.

Uniformed officers and detectives can be seen in the park. Detectives were also seen walking through a nearby tunnel, which leads to a Metra train station and Soldier Field.

Bicyclists traveled through the tunnel as pouring rain, strong wind gusts and booming thunder hit the area. Two soaking wet, uniformed officers sought refuge in the tunnel, checking out their cell phones large puddles started to form.

On Calumet before the rain, several onlookers, including one with a dog, gazed at the police activity. Pat Christophersen and her daughter, Carly, were among the small crowd. They curiously walked down the block from their high-rise.

Pat Christophersen said her son and his girlfriend had just left her building, rode their bicycles toward the park and saw someone lying on the ground.

She said lots of people walk their dogs around there, including her. That’s where she usually takes her Boxer, Molly. She’s also used to seeing lots of police officers around, as well as Bears fans walking to and from Soldier Field.

Aside from warnings she’s received from her building about garage burglaries in the neighborhood, she knows the shooting of the officer was an isolated incident.

With the recent shootings of police officers all over the country, Christopherson, 60, said that Thursday night’s shooting couldn’t have come at a worse time.

“The cops are here to protect us,” Chistophersen said, as blue lights from a nearby squad car flickered on her face. “They’re not here to be on the defensive.”

Dozens of police officers were outside Northwestern Memorial in the immediate aftermath following the shooting, with a number of them leaving before 9 p.m.