To inhibit the spread of the Covid-19 virus, several governmental guidelines (e.g., social contact, vaccination) were proposed. Whether or not these protective behaviours are implemented often depends on citizens’ risk perceptions which, according to previous research, are formed by social media, news media, and interpersonal communications. However, previous research is limited in two ways. First, research mostly focused on adults, thereby neglecting emerging adults who are less affected but equally needed to adhere to the rules. Second, research mainly measured behaviours at one-time point and studied between-person associations, thereby neglecting short-term within-person effects. We therefore conducted a daily diary study among 208 emerging adults (Mage = 21.63, SDage = 1.15) and examined which communication channels increased Covid-19 risk perceptions (i.e., perceived personal susceptibility and societal severity) and, in turn, individuals’ willingness to get vaccinated and follow Covid-19 rules. The results showed that only news media predicted societal severity on the within-level and that severity, in turn, predicted willingness to get vaccinated and follow rules at the between-level. Additionally, social media predicted interpersonal conversations about Covid-19 at the between-and within-level. Overall, this study highlights the importance of news media in affecting emerging adults’ health perceptions and behaviours during a crisis.