Detecting public emergencies from Web pages has been one of the focuses in the research community, as Web contains plenty of valuable information. In particular, Web information usually exhibits some spatiotemporal features, which can be utilized to analyze the pattern of public emergencies. In this survey paper, we review the state-of-the-arts of Web-based detection of public emergencies, including current prototypes and academic research results. After that, we emphasize some research challenges for the detection of public emergencies from Web pages. Finally, a framework to detect public emergencies from Web is presented. Its architecture as well as basic solutions for some critical issues are investigated. This paper is expected to provide some new prospective for the study on public crisis management and emergency decision in the Web and information era.