Police closed Bangor High Street following reports of an explosion on Wednesday.
Shoppers and cafe goers were stunned when a large bang was heard at about 3.45pm.
Passers-by reported a "huge fire ball" and heard a large bang between the Beresford Adams estate agents and Costa coffee shop on the High Street at 3.45pm.
The explosion, is thought to have come from an area which was cordoned off as part of work being carried out.
Pictures of Bangor High Street after explosion. Images by Kerry Roberts
Businesses and shops along the street, including the North Wales Chronicle, experienced an interruption to their electricity supply.
Two fire engines with crews from Beaumaris and Bangor are on the scene.
The police are urging the public to stay away from the area, whilst investigations are going on.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here