Scroll down for further information on this incident!

UPDATE 3/8/08:

This photo has caused a bit of controversy (although not quite as much as the Beer Spill. Visitors have said that it is not concrete, but rather, Stone, Limestone, Marble, or Granite. Christian M. even sent a link showing similar blocks of marble being trucked. The only thing I can say with certainty is that the original source said that it was concrete. My vote is for Limestone. One visitor tells me that they use a giant forklift to get them into the truck. Very cool!

UPDATE 4/13/08:

Chris L. says "I load those containers onto trucks and trains for a living. There's a reason why we load them with the doors facing rearward. Apparently in China they don't follow that procedure."

And John M. gave this some serious thought.
"Much more likely to be marble then limestone. Marble is shipped in blocks for sculptures or for further processing - cutting into sheets and polishing.
Marble also has a low friction factor, so would slide under moderate braking. Also the low friction would make it "easy" to push the block into the container.
In Asian countries serious overloading is a part of life - partly helped by low speeds which means tyres will not blow out as readily because less heat is built up in them.
Normally of course containers are loaded with the doors to the rear to facilitate unloading - why this is back the front is a mystery unless that was the only way they could spread the load the way they needed.
In any case the block was obviously not restrained to any degree, so under braking it slid forward, the impact load on the doors caused them to burst open, and it slid out until stopped by the cabin.
Note the other products suggested have high friction factors so would be unlikely to slide - and granite cannot be white."