A leak-sealing device for sealing a leak in a container, a tank and/or a pipe includes a housing-type carrier unit, at least one expandable sealing member provided on an end region of the carrier unit, which does not expand, or only a little, in the storage position thereof, and at least one fluid connection and/or at least one fluid-release unit which is coupled to the carrier unit in such a way that, during the supply of fluid, the leak-sealing member is at least partially filled and expanded with the fluid in the sealing position thereof by means of a fluid supply. A method for sealing a leak using the leak-sealing device and to a system including the leak-sealing device and a fluid-supply device utilizes a release unit for fluid release.