An annular barrier to be expanded in an annulus between a well tubular metal structure and an inside wall of a borehole downhole for providing zone isolation between a first zone and a second zone of the borehole, comprising - a tubular metal part for mounting as part of the well tubular metal structure, - an expandable metal sleeve surrounding the tubular metal part, each end of the expandable metal sleeve being connected with the tubular metal part, - an expandable space between the expandable metal sleeve and the tubular metal part, and - an expansion opening in the tubular metal part through which fluid enters in order to expand the expandable metal sleeve, wherein the annular barrier further comprises a pressure-intensifying unit having a first bore and a piston unit, the first bore having a first bore part with a first inner diameter (ID 1) and a second bore part with a second inner diameter (ID 2), the piston unit having a first piston with a first outer diameter (OD 1) corresponding to the first inner diameter and a second piston with a second outer diameter (OD 2) corresponding to the second inner diameter, and the second piston being connected to the first piston by means of a connecting rod, which connecting rod has a smaller outer diameter than the second piston, the first outer diameter being smaller than the second outer diameter, the first bore part having a first opening in fluid communication with the expansion opening through a first fluid channel, a first non-return valve being arranged in the first fluid channel allowing fluid to enter the first opening, the first bore having a second opening fluidly connected with a part of the first fluid channel upstream of the first non-return valve, the first bore part having a third opening in fluid communication with the expandable space through a second non-return valve, the second bore part having a fourth opening for entry of fluid in order to allow the first piston to move in a first direction, ejecting fluid through the third opening and into the expandable space, and for exit of fluid in order to allow the first piston to move in a second direction opposite the first direction, and wherein the second bore part has a fifth opening in fluid communication with the fourth opening through a second fluid channel, and a sequence piston surrounding the connecting rod and having a first sequence position in which the sequence piston prevents fluid communication between the second opening and the fifth opening and a second sequence position in which the sequence piston allows fluid communication between the second opening and the fifth opening in order to move the piston unit in the first direction. - a tubular metal part for mounting as part of the well tubular metal structure, - an expandable metal sleeve surrounding the tubular metal part, each end of the expandable metal sleeve being connected with the tubular metal part, - an expandable space between the expandable metal sleeve and the tubular metal part, and - an expansion opening in the tubular metal part through which fluid enters in order to expand the expandable metal sleeve, wherein the annular barrier further comprises a pressure-intensifying unit having a first bore and a piston unit, the first bore having a first bore part with a first inner diameter (ID 1) and a second bore part with a second inner diameter (ID 2), the piston unit having a first piston with a first outer diameter (OD 1) corresponding to the first inner diameter and a second piston with a second outer diameter (OD 2) corresponding to the second inner diameter, and the second piston being connected to the first piston by means of a connecting rod, which connecting rod has a smaller outer diameter than the second piston, the first outer diameter being smaller than the second outer diameter, the first bore part having a first opening in fluid communication with the expansion opening through a first fluid channel, a first non-return valve being arranged in the first fluid channel allowing fluid to enter the first opening, the first bore having a second opening fluidly connected with a part of the first fluid channel upstream of the first non-return valve, the first bore part having a third opening in fluid communication with the expandable space through a second non-return valve, the second bore part having a fourth opening for entry of fluid in order to allow the first piston to move in a first direction, ejecting fluid through the third opening and into the expandable space, and for exit of fluid in order to allow the first piston to move in a second direction opposite the first direction, and wherein the second bore part has a fifth opening in fluid communication with the fourth opening through a second fluid channel, and a sequence piston surrounding the connecting rod and having a first sequence position in which the sequence piston prevents fluid communication between the second opening and the fifth opening and a second sequence position in which the sequence piston allows fluid communication between the second opening and the fifth opening in order to move the piston unit in the first direction.