UTV News is reporting that Army bomb experts are being sent to the scene of the small explosion in Belfast Cathedral quarter.
There are reports that restaurants and other premises in the area are being evacuated.
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Police have raided another address in Moss Side as they investigate the Manchester Arena attack.
A band of heavy, thundery showers moves in from northern France this afternoon.
Armed police were out in force as runners competed in the largest public event in the city since Monday's terror attack.