A man was taken to hospital with a head injury following a 'disturbance' involving 20 people in Piccadilly Gardens.
Police were called to the area at around 6.15pm on Tuesday evening (August 3) to reports that a large group had gathered.
Around 20 people were involved in the fracas, GMP said.
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A man, aged 20, is believed to have been attacked by another man and was taken to hospital with a head injury.
He was later discharged.
A woman was also treated for minor injuries at the scene.
Piccadilly Gardens was cordoned off by police on Tuesday night.
Witnesses described hearing screaming near to the Yorkshire Building Society and near the food market stalls.
An investigation has ben launched by GMP with enquiries said to be ongoing.
No arrests have been made.
A spokesperson for GMP said: "Officers were called at about 6.15pm on 3 August to reports of a disturbance involving about 20 people in Piccadilly Gardens, Manchester.
"It is believed a 20-year-old man was attacked by another man and needed hospital treatment for a head injury, but was later discharged.
"A woman was also treated at the scene for minor injuries.
"Enquiries are ongoing and no arrests have been made."
