We study the kinetics of vapor-liquid and vapor-solid phase separation of a hydrodynamics preserving three-dimensional one-component Lennard Jones system in the presence of an external gravitational field using extensive molecular dynamic simulation. A bicontinuous domain structure is formed when the homogeneous system near the critical density is quenched inside the coexistence region. In the absence of gravity, the domain morphology is statistically self-similar and the length scale grows as per the existing laws. However, the presence of gravity destroys the isotropy of the system and affects the scaling laws. We observe an accelerated domain growth in the direction of the field which resembles a sedimentation process. Consequently, a new length scale emerges which strongly depends on the field strength. Similar behavior is observed in the direction perpendicular to the applied field, with a different growth rate. Finally, the statistical self-similarity of the domain growth and the Porod law in such anisotropic systems is verified in terms of two-point equal time order parameter correlation function and static structure factor.