Despite the growing popularity of ChatGPT and chatbot-assisted writing, research on the use of ChatGPT in second language (L2) writing classrooms remains insufficient. Using reflection papers and focus group interviews, the qualitative study examined doctoral students' views on the impact of using ChatGPT on L2 writing and their expected responses. Thematic analysis revealed that ChatGPT could support writers at the pre-writing, during-writing and post-writing stages and serve as a self-learning tool for writing and thinking development with its human and non-human features. Nonetheless, its generative nature also gave rise to concerns for learning loss, authorial voice, unintelligent texts, academic integrity as well as social and safety risks. Based on the benefits and drawbacks, the doctoral students expected the education sector to make concerted efforts for the effective, ethical and responsible use of ChatGPT in L2 writing. Suggestions are accordingly provided for future considerations in teaching and research to leverage ChatGPT for L2 writing.