Relying on reports in Chinese media, the blog Shanghaiist describes the gaping hole as more than 3,200 square feet in area and almost 30 feet deep, and still expanding.
The Sydney Morning Herald reports that the sinkhole opened up near a subway construction site. Workers noticed that the land was sinking and managed to evacuate the 300 or so people inside the buildings before they collapsed. It is not clear whether the construction caused the sinkhole.
Sinkholes are often caused by the underground erosion of salt beds or soluble sedimentary rocks, such as limestone or dolomite. Groundwater flows through these rocks, creating subterranean caverns that can suddenly collapse.