Famously, the International Court of Justice in the Corfu Channel case affirmed Albania’s international obligation to notify was based on its knowledge, but the Court was silent on the third-party States’ duty to notify impending disasters based on their knowledge. Applying analytical and doctrinal methods, this paper argues that the third-party States’ duty to notify the international community of impending disasters occurring on Earth or in outer space is an emergent norm and should be an erga omnes obligation. Firstly, relying on general international law provisions, including those in environmental and human rights treaties, soft law instruments, principles of cooperation, historical responsibility, and common but differentiated responsibility, this article concludes that the third-party States’ obligation to notify an impending disaster is an emerging norm. Secondly, to support our claim, this article examines the duty to notify provisions in international disaster law and international space law documents. This paper is timely, as both Earth and outer space are becoming increasingly vulnerable to disasters due to human activities, and disaster risks can be prevented and minimized through knowledge-sharing, which should be mandatory. Such obligation on third-party States to notify the international community regarding impending disasters also aligns with global interconnectedness and helps in realizing sustainable development goals.