The big data era is characterized by the emergence of live content with increasing complexities of data dimensionality and data sizes, which poses a new challenge to emergency applications: how to timely disseminate large-scale live content to users who are interested in. The publish/subscribe (pub/sub) model is widely used to disseminate data because of its possibility of expanding the system to Internet-scale size. However, existing pub/sub systems are inadequate to meet the requirement of disseminating live content in the big data era, since their multi-hop routing techniques and coarse-grained partitioning techniques lead to a low matching throughput, and their upload capacities do not scale well. In this paper, we propose a general scalable and elastic pub/sub service based on the cloud computing environment, called GSEC. For generality, we propose a two-layer pub/sub framework to support the dissemination with diverse data sizes and data dimensionality. For scalability, a hybrid space partitioning technique is proposed to achieve high matching throughput, which divides subscriptions into multiple clusters in a hierarchical manner. Moreover, a helper-based content distribution technique is proposed to achieve high upload bandwidth, where servers act as both providers and coordinators to fully explore the upload capacity of the system. For elasticity, we propose a performance-aware provisioning technique to adjust the scale of servers to adapt to the churn workloads. To evaluate the performance of GSEC, about 1,000 servers are deployed and hundreds of thousands of live content items are tested in our Cloud Stack-based test bed. Extensive experiments confirm that GSEC can linearly increase the capacities of event matching and content distribution with the growth of servers, adaptively adjust these capacities in tens of seconds according to the churn workloads, and significantly outperforms the state-of-the-art approaches under various parameter settings.