An early warning system for flash floods in Hoang Su Phi District, Vietnam was developed using a geomorphological and hydrological approach. By analyzing eight basin parameters, a potential flash flood map was created to predict areas at risk. Automatic weather stations provided data for early predictions, allowing for a potential risk map to be generated online. This system can provide warnings for flash floods up to 1-6 days in advance, giving local authorities time to take preventive measures and reduce damages caused by these natural disasters.