Leakproof and liquid-tight packaging box formed from a one-piece blank, said blank comprising: - a base surface forming a horizontal plane, and first folding surfaces for forming the long sides of the box, a crease between the base surface and each first folding surface, vertical surfaces for forming the short sides of the box, a crease between the base surface and each vertical surface, a first corner bellows and a second corner bellows of a corner structure, and an inclined fold between the first and second corner bellows; - a conical fold between the folding surfaces of the long sides of the box and the second corner bellows in such a way that the folding line is inclined with respect to the crease between the base surface and the vertical surface; - second folding surfaces connected to the first folding surfaces via second folding lines, and extending adjacent to and parallel with said first folding surfaces, and horizontal hook locks functioning as a locking means formed on outer end edges of said second folding surfaces; - a stacking plane connected to each of the vertical surface via a crease; - an underside of each said stacking plane connected to said stacking plane via a double crease; and locking slots arranged to receive said hook locks in a locking position at said underside of the stacking plane, wherein said packaging box is formed by means of folding the vertical surface into a vertical attitude from the crease between the vertical surface and the base surface, folding said stacking plane into a horizontal configuration, with said underside folded along the double crease below the stacking plane, and a liquid-tight corner structure is formed by folding the first corner bellows and the second corner bellows together from the inclined fold, and the vertical surface of a short side of the packaging box is formed to be deflected at a slope into the box, becoming essentially conical, by means of the inclined conical fold between the folding surface of the long sides of the box and the second corner bellows, characterized in arranging said horizontal hook locks formed on said second folding surfaces to come between the double crease and lock horizontally into the locking slots of a short side of the box at said underside of the stacking plane. - a base surface forming a horizontal plane, and first folding surfaces for forming the long sides of the box, a crease between the base surface and each first folding surface, vertical surfaces for forming the short sides of the box, a crease between the base surface and each vertical surface, a first corner bellows and a second corner bellows of a corner structure, and an inclined fold between the first and second corner bellows; - a conical fold between the folding surfaces of the long sides of the box and the second corner bellows in such a way that the folding line is inclined with respect to the crease between the base surface and the vertical surface; - second folding surfaces connected to the first folding surfaces via second folding lines, and extending adjacent to and parallel with said first folding surfaces, and horizontal hook locks functioning as a locking means formed on outer end edges of said second folding surfaces; - a stacking plane connected to each of the vertical surface via a crease; - an underside of each said stacking plane connected to said stacking plane via a double crease; and locking slots arranged to receive said hook locks in a locking position at said underside of the stacking plane, wherein said packaging box is formed by means of folding the vertical surface into a vertical attitude from the crease between the vertical surface and the base surface, folding said stacking plane into a horizontal configuration, with said underside folded along the double crease below the stacking plane, and a liquid-tight corner structure is formed by folding the first corner bellows and the second corner bellows together from the inclined fold, and the vertical surface of a short side of the packaging box is formed to be deflected at a slope into the box, becoming essentially conical, by means of the inclined conical fold between the folding surface of the long sides of the box and the second corner bellows, characterized in arranging said horizontal hook locks formed on said second folding surfaces to come between the double crease and lock horizontally into the locking slots of a short side of the box at said underside of the stacking plane.