  Numerical simulations of outflows formed during the collapse of 100 M_sun
cloud cores are presented. We derive a generalised criterion from MHD wind
theory to analyse the launching mechanism of these outflows. The criterion is
successfully applied to the whole outflow structure and cases with
sub-Keplerian disc rotation. It allows us to decide whether an outflow is
driven centrifugally or by the toroidal magnetic pressure. We show that
quantities such as the magnetic field line inclination or the ratio of the
toroidal to poloidal magnetic field alone are insufficient to determine the
driving mechanism of outflows. By performing 12 runs we are able to study the
influence of the initial conditions on the properties of outflows around
massive protostars in detail. Our simulations reveal a strong effect of the
magnetic field strength on the outflow morphology. In runs with weak fields or
high rotational energies, well collimated, fast jets are observed whereas for
strong fields poorly collimated, low-velocity outflows are found. We show that
the occurrence of a fast jet is coupled to the existence of a Keplerian
protostellar disc. Despite the very different morphologies all outflows are
launched from the discs by centrifugal acceleration with the toroidal magnetic
field increasingly contributing to the gas acceleration further away from the
discs. The poor collimation of the outflows in runs with strong fields is a
consequence of the weak hoop stresses. This in turn is caused by the slow
build-up of a toroidal field due to sub-Keplerian disc rotation. The mass
ejection/accretion ratios scatter around a mean of 0.3 in accordance with
observational and analytical results. We suggest an evolutionary scenario for
the earliest stage of massive star formation in which initially poorly
collimated outflows develop which progressively get better collimated due to
the generation of fast jets.
