Galway City Hall has been extensively damaged by an explosion, which happened inside the building shortly before 8am.
Gardaí and City Council staff say the cause of the explosion has not yet been established, but the possibility of an exploding water boiler is being investigated.
Bord Gáis has said the building is not serviced by natural gas.
A number of windows were blown out and damage was caused to the ground floor of the College Road building.
About a dozen of the 200 city hall staff were in the building at the time but none were injured.
A spokesman for the City Council said the building will remain closed until a full investigation takes place.