Chicago police are warning Chatham and Gresham residents about a string of carjackings that occurred in recent weeks in the South Side neighborhoods.

In each incident, one or two men in their early 20s approached people as they were getting out of their vehicles and demanded the keys, Chicago police said. They struck someone in the head with an unknown weapon in one of the robberies.

The carjackings all happened in the late night or early morning hours, police said. They happened:

· July 31 in the first block of West 81st Street;

· Aug. 10 in the 7900 block of South Vincennes Avenue;

· Aug. 11 in the first block of West 79th Street; and

· Aug. 14 in the 7900 block of South Vincennes Avenue.

Anyone with information about these robberies is asked to call Area South detectives at 312-747-8273.

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