An armed robber has struck three times since last month in the South Side Grand Crossing neighborhood, including two hold-ups in the same block that happened over a 90-minute span.

In each incident, the man has approached victims, displayed or implied that he had a weapon and announced a robbery, according to a community alert from Chicago Police.

The most recent robbery happened at 7 a.m. Thursday in the 7300 block of South Dorchester, police said. The other two happened on Aug. 26 in the 7200 block of South University, one at 10:02 a.m. and the other at 11:30 a.m.

The suspect was described as a black man with a dark complexion between 20 and 29 years old, standing 5-foot-6 to 5-foot-10 and weighing 150 to 180 pounds, police said.

Anyone with information about the robberies is asked to call Area Central detectives at (312) 747-8380.