This warning comes just six months after Paris was chosen to be the host of the 2024 Olympics.
This overspend was reported by government experts, who said the building projects could exceed forecasts by half a billion euros on a total planned budget of 6.8 billion euros.
They also warned of possible delays in completing the Olympic village.
At this stage, 3.8 billion euros of the budget comes from private funds. But this report focuses on the remaining 3 billion euros, which is the construction budget and includes 1.5 billion euros of state investment.
The report raised questions about the planned Olympic village by the river Seine, in the north of Paris. This is intended to accomodate 10,000 competitors and then become 3,000 housing units. It also queried the necessity of a village to accommodate visiting journalists.