A centuries-old wall at San Anton Palace collapsed into the parking area used by the President's staff at around 2.45am on Wednesday.
Debris fell on to the parked vehicles, although fortunately at that time in the morning, there were not many there. Nobody was hurt in the incident.
The wall was being restored over the summer.
Magistrate Simone Grech is leading an inquiry into the wall's collapse, and the gardens have been temporarily closed to the public as a safety precaution.
The Office of the President issued a brief statement at 11.25am, giving hardly any information about the collapse but confirming that the Restorations Directorate is looking into the technical side of the matter. Its head, Norbert Gatt, was on site in the morning.
San Anton Palace has been the official residence of the President of Malta since 1974. It was originally built in the early 17th century as a country villa for Antoine de Paule, a knight of the Order of St John.
The palace is surrounded by the extensive San Anton Gardens, parts of which have been open to the public since 1882.