Based on a social action research, this article discusses the collective action taken by inhabitants of Chinese and South-East Asian origin in a north-eastern suburb of Paris: targeted by violent attacks, these residents occupied the public space at the base of their residences and demanded the intervention of public authorities. In recounting the different steps of the mobilisation, this article demonstrates how an ethnocentric dynamic was created around security issues and how an ethno-spatial minority was formed within the neighbourhood and the city. It also shows in what conditions this ethno-security action transforms itself into an associative and citizen commitment within the neighbourhood and the city and modifies the perceptions of the actors, their capacity for action and their relations with the neighbourhood and with politics. At the intersection of several fields of research, including the sociology of migration, urban sociology and political sociology, the article shows how ordinary inhabitants of Chinese and South-East Asian origin participate in their neighbourhood's local civic life.