Clarifying the hydro-mechanical characteristics of the mechanism associated with mass remobilization is a major step towards landslide early warning, but this clarification is usually hampered by a lack of in situ evidence. In this study, shallow rainfall-triggered slope failures under partially saturated conditions were documented by combining instrumental evidence from field experiments on a natural co-seismic landslide and hydro-mechanical slope stability analysis in an earthquake-affected region. The results revealed the transient processes and unsaturated conditions associated with mass movement in response to rainfall, and preferential flow paths were found to dominate the hydrological processes during rainfall infiltration in the landslide deposit. The results also demonstrated the importance of certain hydrological parameters, including soil matric suction and moisture content, in landslide early warning. This study reveals a partially saturated hydro-mechanical behaviour to predict the initiation of rainfall-induced landslides during post-earthquake disaster relief.