At least five workers were killed and one remained missing after a rooftop and scaffold collapsed in China's Hunan province, local authorities said Saturday.The collapse occurred at around 5.10 p.m. Friday when 11 workers were finishing construction work at a machine repair workshop of a local nonferrous metal company, reported Xinhua.Five workers were pulled out of the debris and rushed to hospital immediately. Rescue work is still under way.The cause of the accident is still being investigated.