Process and ultracompact plant for continuous production of hot rolled steel strip comprising an ingot mould (15) which produces a very thin slab at a speed between 4 and 16 m/min, wherein the thickness of the narrow sides is between 15 and 50 mm with a central swelling. Such slab has a core in which the steel is still liquid; it is run through a vertical pre-rolling device (16) which reduces the thickness of the slab, flattening it. The solidified slab can thus undergo a first light rolling process using a pinch roll (17) and, by forming a free curve, it moves to a horizontal position where it can undergo a second light rolling process by another pinch roll (22′). A heating process (if required) includes an inductor (50). A superficial descaling process and a series of reductions in a rolling mill made up of at least three stands (20′, 20″, 20′″) are provided maintaining a slab temperature along the train above the Ar3 recrystallization point. Downstream of the rolling mill, there is a conveyor (31) with cooling showers (32), flying shears (33) for cutting the strip to the required size, pinch rolls and at least two coilers (34) for forming coils of the hot rolled strip.