Under COVID-19, because of extensive online learning and the use of the internet for communication, there is a risk of intensification of Internet addiction (IA) in young people. Unfortunately, there are very few related studies in different Chinese contexts, including Hong Kong. In this study, we examined several research gaps in the literature with reference to university students in Hong Kong: a) prevalence of IA; b) socio-demographic factors related to IA; c) relationships between IA and other mental health problems and stressors (i.e., comorbidity); and protective factors for IA. To address the above research issues, we conducted an online survey in early 2021 (N = 1,648) using validated instruments on IA, psychological well-being, and stress. Based on the Young Internet Addiction Scale, roughly half of the respondents could be considered as showing excessive IA symptoms. Regarding demographic correlates of IA, younger students and those who experienced personal financial difficulty showed higher IA levels, and there was no observed gender difference. There were positive relationships between IA symptoms and mental health problems (depression, post-traumatic stress disorder, suicidal behavior, and hopelessness) and stresses (difficulties encountered and unmet psychosocial needs), suggesting co-morbidity of IA. IA was also negatively associated with positive psychological attributes such as flourishing and emotional competence, which could be regarded as factors protecting young people from IA. Results are discussed with reference to the different ecological risks and protective factors in IA amongst young people in the Chinese context.