A building near my apartment bears this strange scar near its top.
This is 50ft or so up. And each segment of this cladding is about 3ft x 2ft, and made of some sort of metal. It's going to take a really hefty clout to crumple it this badly.
I think this must have happened in situ. A crane would seem to be the only likely culprit - although I'm not aware of any tall cranes operating in this vicinity, and I have lived here or hereabouts for the whole of my 10 years in Beijing.
Safety in crane operation does not seem to be very impressive in China. Only a few months ago, I saw two super-tall cranes over in Sanlitun smack their booms into each other. Luckily, no serious damage appeared to result; but it was quite a heavy collision. You would think, wouldn't you, that you wouldn't normally place two such large cranes in such proximity that they could hit each other? And if occasionally this is necessary, you'd think that there would be procedures for ensuring that they will not both be rotating at the same time. And if they are rotating at the same time, you'd think they'd at least try to make sure they rotated in the same direction. And heck, if they must contra-rotate, you'd think their operators would keep an eye out to make sure that they weren't going to come into contact with each other. But where would be the fun in that?? Oh, no: this is China. If it is possible to come up with a really stupidly unsafe way of doing something, you can rely on the Chinese worker to find it.