The aim of the present study was to examine the role of out-group threats in fostering one-group perceptions directly and indirectly via post-traumatic stress symptoms in the aftermath of a natural disaster. We also tested whether these relationships differ depending on the ethnic group of belonging (majority vs. minority). Participants were 589 Italians and 122 immigrants from a region strongly affected by the earthquakes that struck Northern Italy in 2012. Results revealed that among Italians threat stemming from negative out-group behaviour was associated positively with post-traumatic stress symptoms and negatively with perceptions of being a common group with immigrant survivors. Among immigrants, threat posed by the out-group for economic resources was positively associated with post-traumatic stress symptoms and, indirectly, with higher one-group perceptions.