Police were called to Anderson’s Meadow, off Mile Cross Road, in Norwich, following the discovery of an unexploded bomb.
Officers were called at 12.50pm on Monday after the device, believed to be a Second World War mortar, was found by a workman.
Police worked with staff from landowners Norwich City Council and a cordon has been put in place as a precaution.
The Explosive Ordnance Disposal (EOD) was contacted and arrived on scene to assess the item.
The public were asked to avoid the area while the device was safely contained and assessed.
Norfolk Police uploaded a video to Twitter of the mortar being exploded saying it was detonated "loudly but safely".
Officers now appear to have left the scene with a cordon around the site and a shell on the ground.
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