The study focused on Hong Kong mathematics teachers’ personal experiences and challenges in online teaching during the COVID-19 pandemic crisis. A SWOC analysis is adopted. Results showed that they tried to offer e-learning as an alternative mode of teaching to maintain the education service within the pandemic. Hong Kong teachers tended to focus on external factors rather than internal factors in the initial period of online teaching. They agreed that there was a paradigm shift in the role of teaching during the crisis. They were commonly building a sufficient level in using technology, but this was not equivalent to be competent in achieving instructional goals. Mathematics teachers’ professional knowledge is influenced by their personal online teaching experiences. Their attitudes and beliefs are crucial factors in the role and effectiveness of using online teaching. Copyright © 2021 left to authors.