A portable flood barrier section is located on a ground (2) to form a barrier (3) against flooding water (4), comprising an erectable wall (5) which along one of its edges (6) is hinged to a basis. The hinge (7) enables a rotating erection (A) of the wall (5) from an essentially horizontal position to an erected position. A flexible or rigid tie (8, 9), which extends from the basis to the wall (5) on the flooded side (10) of the wall (5), prevents an erection of the wall (5) beyond the erected position. A seal (12) is in the erected position of the flood barrier section (1) located between the flood barrier section and the ground (2). The flood barrier section (1) is adapted to, prior to flooding, to expose the seal (12) to a positive sealing pressure exceeding a pressure caused by the weight of the flood barrier section (1). The invention also relates to a flood barrier (3) comprising flood barrier sections (1).