A 17-year-old was stabbed in his leg in Preston.
Waterstones in Fishergate and Home Bargains in Market Place, Cheapside were taped off last night.
Police have launched an investiagtion to arrest the attacker.
Officers responded to calls that a man had been spotted in the city centre with a knife at around 5.45pm.
Paramedics also attended to the victim in Cheapside whose injuries are not life-threatening.
Detective inspector Steve Monk, of South CID, said: “I appreciate this will have caused distress and concern to those who witnessed it and I would reassure people that we are treating this as an isolated incident and an investigation is underway to identify and arrest the offender.”
Anyone with information should call police on 101 quoting log number 1070 of Saturday, September 8 or independent charity Crimestoppers on 0800 555 111.