Rapid urban metabolism is causing many resources to flow from consumption to waste. But many of these wastes could be secondary resources, and cities could become urban mines and an increasing supply of future resources. Hong Kong, one of the most developed and populated cities in the world, has demonstrated a completely metabolic evolution to be an urban mine, since the 1970s. Covering 14 types of e-waste and eight types of end-of-life vehicles, this study first investigates Hong Kong’s evolution as an urban mine. The potential output weight of the urban mine quickly grew from 117 kt in 2000 to 368 kt in 2014, and it is estimated to remain in the range of 300–350 kt over the years 2015–2050, with 40–50 kg/cap/year. The economic potential of urban mining, for 18 metals, plastic, glass, and rubber tires, will be approximately US$2 billion annually, mainly contributed by precious and rare metals. All the obtained results contribute to Hong Kong’s waste management and promise to have positive impact on urban mining and circular economy for other, less-developed cities or regions.