The child has been rushed in a helicopter to Southampton General Hospital, which specialises in serious head injuries.
It is not known how the boy fell from the roof, but he is said to be in a critical condition.
The incident took place at the city’s Crasswell Street car park hat around 8.40am this morning.
A huge emergency services presence could be seen as an air ambulance landed at the nearby car park next to Cascades Shopping Centre.
A spokeswoman for Hampshire Constabulary confirmed: “We were called at 8.10am this morning (12 June) to a report that a boy had fallen from the roof of the car park.
“He has been airlifted to Southampton General Hospital.”
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