An electric fire developed at the reception area at Castille and while this was immediately put out, smoke engulfed the area for some time, Civil Protection Department sources said.
In a statement, the Office of the Prime Minister said the fire resulted from an accidental short circuit.
An inquiry will take place since the fire broke out at a public building.
The reception is situated at street level with its entrance being in St Paul's Street.
The Emergency services received the report after 11am and the building was evacuated immediately. No one was injured.