One problem for public safety organizations in a disaster is the management of response activities and their dependencies on an intra-and inter-organizational level. Our interviews with end users have shown that current solutions for managing activities are complicated to use in the crisis by teams in the field and also in operation centers, when facing continuous unexpected events and cross-organizational activities. We propose an activity centric system for managing crisis response activities for such situations. We give an example how this system is used in a crisis within one organization and cross-organizations. Afterwards, we explain the evaluation of the solution. This research contributes not only to the crisis management domain, but also to the business process management domain by providing an alternative view on activities in highly dynamic scenarios.