One person is in stable condition in hospital after being stabbed at London Drugs around 8:11 p.m. on Saturday evening.
Police said the accused will be arrested after being treated in hospital.
The suspect was injured when witnesses confronted him in the store, according to police.
Ages of the victim and accused were not immediately available.
Several police vehicles surrounded the London Drugs on Saturday and officers were interviewing customers in the store, and turned away potential customers who approached.