Police said a stabbing was reported at around 1:49 p.m. at Homeplus' Guwol store in the western port city, and a man reportedly in his 60s was arrested at the scene.
The suspect reportedly wielded a knife while moving on an escalator from the second basement level to the second floor, which houses other shops, before being restrained by shoppers.
One of the injured people suffered cardiac arrest and was transported to a hospital for treatment.
Police are investigating the incident, while further details about the victims' conditions were not immediately available.
Authorities have yet to determine the suspect's motive or provide additional information about the incident.
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