A 13-year-old girl has been arrested after a shopping trolley was allegedly tossed off a railing at a shopping centre on Sydney's north shore, hitting and injuring a 59-year-old man.

Emergency services responded to reports at 11.50am that a man was seriously injured after being struck by a shopping trolley while walking on the ground floor of a Chatswood shopping centre on Victoria Avenue.

The man was treated at the scene for head and facial injuries before he was taken to Royal North Shore Hospital in a stable condition.

A 13-year-old girl was arrested at the scene and was taken to Chatswood Police Station for questioning.

Police have seized the shopping trolley for forensic examination.

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