CHICAGO (CBS) — Police are warning people after a series of overnight downtown robberies over the past two weeks.

The robberies took place between June 20 and 30.

The victims were attacked while walking on the sidewalk and their property forcibly taken by a group of young men.

The robberies have occurred at:

• 42 E. Adams on June 20 at 1:50 a.m.;
• 71 W. Van Buren on June 21 at 1:15 a.m.;
• 180 N. Wabash on June 26 at 11:40 p.m.; and
• 160 N. Wells on June 30 at 12:43 a.m.

Descriptions of the offenders vary, but they have been described as black males in their late teens to early 20s, police said.