A cordon is in place in Piccadilly Gardens after reports of a suspicious package were made.
A spokesperson for GMP confirmed: “A man aged 26 has now been formally arrested and is in custody.
“Transport links including the Metrolink have been affected as a result of the cordon.
“The suspicious package in Piccadilly Gardens is not believed to be a viable device.
“The fire service is currently at the scene to assist with enquiries.
“A cordon will remain in place until the materials are made safe to move and enquiries have concluded.
“The 26-year-old man remains in custody for questioning.
“As part of enquiries, Oldham Library has also been evacuated after reports of a suspicious device found there.
“Officers are keeping an open mind and are exploring the possibility the incidents are linked.”