An off-duty Chicago police officer was ambushed and shot Monday, the second officer shot in the city in as many days following a violent weekend, authorities said. 

The incident happened in the 8900 block of South Stoney Island when the unidentified officer was in his personal vehicle at a stoplight around noon when two gunmen opened fire into the vehicle, Chicago Police Superintendent David Brown said in a news briefing. 

"We heard some rumors of a carjacking but we don’t know yet," Brown said. "The circumstances suggest several different scenarios of what this might be."

The officer, a four-year veteran of the force, was struck in the lower torso and put inside the squad car of responding officers and taken to a hospital, Fox 32 Chicago reported. He underwent surgery and was "doing well," Brown later tweeted. 

Chicago Police Superintendent David Brown talks to reporters about an off-duty officer who was shot Monday.  (Chicago Police Department)

Investigators were searching for possible video surveillance and witnesses to the shooting. The search for the suspects is ongoing. 

Monday's shooting of a police officer follows another that occurred Sunday. A police sergeant was standing in a parking lot on the city's South Side when he was struck by a bullet, authorities said. He suffered a graze wound to the chin and was treated and released from a hospital. 

The sergeant was the first Chicago police officer shot this year, though 12 others have been shot at but weren't struck, Brown said. In all, 38 people were shot and five people were murdered over the weekend, according to police. 

In one incident, two people were killed and 13 were wounded early Sunday in a possible gang-related shooting, police said. 

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In another Monday tweet, Brown said "there must be real consequences for violent offenders who choose to engage in gun violence not just against our officers, but all residents of our city."