The provincial police watchdog is investigating after two seniors and an 18-year-old man were injured during an incident with police at a St. Catharines variety store on Sunday.

The Special Investigations Unit says Niagara police got a call about an "incident" at a store on the corner of Arthur Street and Northglen Avenue.

Officers showed up and a Taser was discharged, police say. The SIU didn't say why police were originally called there, or why the Taser was used.

An 18-year-old man was rushed to hospital after the incident in serious condition. A 77-year-old man and a 75-year-old woman were also taken to hospital with minor injuries.

The SIU did not say who was Tasered, or how the injuries were sustained.

Four SIU investigators and two forensic investigators have been assigned to investigate the incident.

The SIU investigates reports involving police where there has been a death, serious injury or allegations of sexual assault.