There has been a sharp increase in the number of robberies in part of Leicester, say police.
Eleven people - mostly Asian women who were alone - have been attacked in the Spinney Hill and Stoneygate areas in the past two weeks.
Mobile phones or jewellery have been snatched from the victims, some of whom have been hurt.
Police have urged local people to be vigilant and to avoid unnecessarily carrying valuables.
The robberies occurred in busy places, but few witnesses have come forward, according to Insp Bill Knopp.
He said: "It may be that passers-by have not realised what was happening.
"We are now asking that people in the area are vigilant, and phone us immediately if they see anything suspicious.
"This could include groups of men following individuals, or an actual attack taking place."
A number of the victims have been hurt during the attacks, though not seriously.
Insp Knopp added: "Some have had difficulty in making the initial report to police because English is not their first language, which is another reason why immediate information from witnesses could be vital."