SHOPPERS have been attacked with a "CS gas-like substance" at Selfridges as a man was arrested at the Oxford Street store today.
Nine people were treated at the scene with a man in his 20s arrested on suspicion of affray in London.
One shocked witness today told The Sun she had been shopping when she heard a "loud bang".
Carly Harrison, 34, said: "My friend went over to see what had happened, but came back saying she couldn't breathe, she said it was like she was being suffocated.
"She started coughing, then I started coughing, and then the other shoppers near us started coughing too - it was like something out of a scary movie, a ripple across the shop floor."
Panicked, the two women fled out the fire exit to fresh air.
She added: "People were evacuated from the shop, and people were really freaked out and crying, it was horrible."
Met Police confirmed they had been called to the scene just after 1.30pm.
A spokesperson said: "It was reported that a man, in his 20s, had been detained by security staff after he sprayed another man with an unknown substance, which caused similar effects to CS gas.
"The man was arrested on suspicion of affray. He has been taken into custody.
"A group of nine members of the public have been treated at the scene for effects of the spray."
Exposure to CS gas can cause watering eyes, chest tightness, coughing and sneezing.
People were really freaked out and crying, it was horribleCarly Harrison
Selfridges said the incident had unfolded after a "short altercation between two males" - with the irritant sprayed during the chaos.
A spokesperson said: "The ambulance service are confident it is a non-harmful irritant.
"A few team members and customers were checked over by the ambulance service for irritated nose and throat, with all but one being given the all clear.
"One customer continues to be monitored.”
The spokesperson confirmed the store remained open and was trading as normal.
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Photographs appeared to show paramedics using water to treat members of the public.
Selfridges is a Grade II listed retail premises on Oxford Street in London.
The London Ambulance Service has been contacted for comment.