The recent COVID-19 pandemic prompted the implementation of online teaching and online assessment. Online assessment can be challenging to both teachers and students due to technical, academic, and ethical issues. In this survey, we adopted both qualitative and quantitative approaches to evaluate (1) the perceived effectiveness of online assessment; (2) barriers and problems of using online assessment; and (3) suggestions for improvement. The online survey was conducted in May 2020, 752 full-time undergraduate and postgraduate students had completed the questionnaires. Forty-three undergraduate students attended an individual interview between May and June 2020. A total of 739 (98.3%) students had the experience of taking online assessment during COVID-19 outbreak. The survey results revealed that only 16.6% of students were satisfied with their online assessment arrangements. The major difficulty that students encountered was technical problems (52.6%). Majority of students (72.6%) agreed that online assessments were more affected by computer problems and internet connection when compared with traditional examination. Students expressed that teachers' feedback was essential for their learning, and they wished to receive timely and detailed feedback on their performance. Students suggested that technical support should be provided, and standardized measures should be taken to ensure academic honesty.