The hottest market in the hottest economy in the world is Chinese real estate. The big question is how vulnerable is this market to a crash.

One red flag is the vast number of vacant homes spread through China, by some estimates up to 64 million vacant homes.

We've tracked down satellite photos of these unnerving places, based on a report from Forensic Asia Limited. They call it a clear sign of a bubble: "There’s city after city full of empty streets and vast government buildings, some in the most inhospitable locations. It is the modern equivalent of building pyramids. With 20 new cities being built every year, we hope to be able to expand our list going forward."