Recent attention on ChatGPT, a prominent AI language model, highlights its potential in assisting EFL writing. Although ChatGPT's capabilities involve grammar correction, vocabulary enrichment and sentence structuring, its full potential alongside human scaffolding in EFL writing classrooms remains unexplored. This study aims to fill this gap by adopting the cognitive process model of writing as a theoretical framework. Four groups of 19 EFL learners were engaged in think-aloud sessions and interviews. The collaborative writing process with ChatGPT progressed through iterative stages of planning, translating, and reviewing, incorporating various embedded subprocesses. Guidance from the teacher and collaborative work among peers facilitated the effective use of ChatGPT for writing refinement by creating an environment of emotional reassurance and enhancing metacognitive awareness among the learners. The findings emphasise the importance of collaborative work, orchestrated by the teacher and peers in using ChatGPT in the EFL writing class.