The accident took place at the Huacaotan Coal Mine in Zhangye City on Thursday night.
The last deceased worker was lifted from a deep shaft earlier today after rescuers pumped water from the bottom of the shaft, state-run Xinhua news agency reported.
The workers fell off the platform after it overturned more than 200 metres above the bottom of the shaft, which was inundated by deep water, authorities said.
The coal mine, which was under construction when the accident happened, belongs to Zhangye Hongneng Coal Industry Ltd.