§1. When a parish becomes vacant or a pastor has been impeded from exercising his pastoral function and before the appointment of a parochial administrator, the parochial vicar is to assume the governance of the parish temporarily. If there are several vicars, the one who is senior in appointment or, if there are no vicars, a pastor determined by particular law assumes this governance.
§2. The one who has assumed the governance of a parish according to the norm of §1 is immediately to inform the local ordinary about the vacancy of the parish.
Source: Code of Canon Law (Vatican.va)