A 16-year-old girl had her handbag stolen while outside Leyland Market.
The victim was at a cafe at the market, on Northcote Street, when she put down her bag on a table and briefly left it unattended while she ran after a child.
When she returned, her brown leather handbag had been stolen.
It contained a black purse with a letter ‘G’ on the front and a set of house keys.
Police are asking people to be vigilant and to attempt to keep their bags with them at all times.
Officers are looking at CCTV images taken from outside the market in a bid to catch the thief.
Anyone with information is asked to call 0845 1253545 or Crimestoppers anonymously on 0800 555 111.