The prefect is the general representative of the national government in each province, and works under the supervision of the Minister of the Interior (Home Secretary), of which the prefecture is a department. As such, he performs all the state and local administrative functions and duties (accruing to the Ministry of the Interior, but at a provincial level) that are not delegated to other bodies, and guarantees liaison among local authorities and between these authorities and the state.
In emergency situations he may replace local authorities (e.g. replacing the Mayor should the municipal council resign). He is responsible for public order and safety in the province.
To find out more:
Portal of Prefectures – UGT