High-density cities are faced with growing extreme hot weather driven by climate change and local urbanization, but localized heat risk detection is still at an early stage for most cities (Watts et al., 2019). This study developed a spatiotemporal hazard-exposure-vulnerability assessment of the extreme heat risk in Hong Kong for 2006, 2011, and 2016 integrating cumulative very hot day hours and hot night hours in summer, population density and a principal component analysis (PCA) of demo-socioeconomic characteristics. The risk was found spatially variant, and high-risk spots were identified at the community scale for both daytime and nighttime with underlying determinants behind. In both the daytime and the nighttime, high risk mainly occurred in the core urban areas. Nearly 10 more hot-spots were found in the nighttime than those in the daytime. Several old communities in Kowloon stayed at high risk from 2006 to 2016. Some new towns in the New Territories turned to be at higher risk in 2016 compared to 2006 and 2011, and this result showed signs to be emerging hot-spots in the near future. This study would be a useful reference for community-scale heat risk assessment and mitigation for the development of healthy and sustainable high-density cities.