Process for producing high flow heterophasic propylene copolymers; said process comprises the steps of - polymerising propylene and optionally an ethylene and/or C 4 -C 12 alpha-olefin comonomer in a slurry reactor in the presence of hydrogen and a polymerisation catalyst system, obtaining as slurry reactor product first propylene polymer fraction of the polypropylene matrix - transferring the slurry reactor product into a 1 st gas phase reactor - further polymerising propylene and optionally an ethylene and/or C 4 -C 12 alpha-olefin comonomer in the presence of said slurry reactor product, the polymerisation catalyst system and additional hydrogen, obtaining as 1 st gas phase reactor product a mixture of the first propylene polymer fraction and a second propylene polymer fraction, being the polypropylene matrix of the heterophasic propylene copolymer having an MFR 2 in accordance with ISO 1133 (230°C, 2.16 kg) equal to or above 200 g/10min, - transferring said 1 st gas phase reactor product into a 2 nd gas phase reactor - producing a first elastomeric propylene copolymer fraction, in the presence of said 1 st gas phase reactor product and at least one ethylene and/or C 4 to C 12 α-olefin, the comonomer/propylene ratio being in the range of 150 to 300 mol/kmol - transferring the 2 nd gas phase reactor product into a 3 rd gas phase reactor - producing a second elastomeric propylene copolymer fraction in the presence of said 2 nd gas phase reactor product and at least one ethylene and/or C 4 to C 12 α-olefin, the comonomer/propylene ratio being in the range of 300 to 1000 mol/kmol and - recovering the heterophasic propylene copolymer for further processing said polymerisation catalyst system comprising (i) a Ziegler-Natta procatalyst and (ii) an organometallic cocatalyst and (iii) an external donor represented by formula Si(OCH 2 CH 3) 3 (NR 1 R 2) wherein R 1 and R 2 can be the same or different and represent a hydrocarbon group having 1 to 12 carbon atoms. - polymerising propylene and optionally an ethylene and/or C 4 -C 12 alpha-olefin comonomer in a slurry reactor in the presence of hydrogen and a polymerisation catalyst system, obtaining as slurry reactor product first propylene polymer fraction of the polypropylene matrix - transferring the slurry reactor product into a 1 st gas phase reactor - further polymerising propylene and optionally an ethylene and/or C 4 -C 12 alpha-olefin comonomer in the presence of said slurry reactor product, the polymerisation catalyst system and additional hydrogen, obtaining as 1 st gas phase reactor product a mixture of the first propylene polymer fraction and a second propylene polymer fraction, being the polypropylene matrix of the heterophasic propylene copolymer having an MFR 2 in accordance with ISO 1133 (230°C, 2.16 kg) equal to or above 200 g/10min, - transferring said 1 st gas phase reactor product into a 2 nd gas phase reactor - producing a first elastomeric propylene copolymer fraction, in the presence of said 1 st gas phase reactor product and at least one ethylene and/or C 4 to C 12 α-olefin, the comonomer/propylene ratio being in the range of 150 to 300 mol/kmol - transferring the 2 nd gas phase reactor product into a 3 rd gas phase reactor - producing a second elastomeric propylene copolymer fraction in the presence of said 2 nd gas phase reactor product and at least one ethylene and/or C 4 to C 12 α-olefin, the comonomer/propylene ratio being in the range of 300 to 1000 mol/kmol and - recovering the heterophasic propylene copolymer for further processing said polymerisation catalyst system comprising (i) a Ziegler-Natta procatalyst and (ii) an organometallic cocatalyst and (iii) an external donor represented by formula Si(OCH 2 CH 3) 3 (NR 1 R 2) wherein R 1 and R 2 can be the same or different and represent a hydrocarbon group having 1 to 12 carbon atoms. (i) a Ziegler-Natta procatalyst and (ii) an organometallic cocatalyst and (iii) an external donor represented by formula Si(OCH 2 CH 3) 3 (NR 1 R 2) wherein R 1 and R 2 can be the same or different and represent a hydrocarbon group having 1 to 12 carbon atoms.