Man arrested over alleged one-punch attack in central Sydney

A man will front court today following an alleged unprovoked assault in Sydney CBD overnight that left the victim in a serious condition.

Police said a 57-year-old man was walking along George Street just after 7pm yesterday, when a man aged 37 allegedly punched him once in the head.

He fell unconscious backwards, hitting his head on the footpath.

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Police said the younger man fled the scene running towards Sussex Street.

Paramedics treated the injured man at the scene for multiple facial fractures and head injuries, causing the CBD light rail service to be disrupted for about 30 minutes.

He was later taken to St Vincent's Hospital in Sydney in a serious condition. He will be undergoing surgery today.

Police set up a crime scene and following inquiries, officers arrested the 37-year-old man at a nearby hotel on Sussex Street about 3.30am today.

He was charged with reckless grievous bodily harm and refused bail.

He is due to appear before court later today.