About 200 blocks from where I spawned when creating a new world, it starts; Random chunks are spawned 'empty' (bedrock at layer 1, dirt at layer 2, 3, grass at layer 4 - like the superflat world!. So it's not just visual, they actually spawn empty, (i can build in those empty chunks). I walked about 500 blocks in 1 direction from where the bad chunks started, and the empty chunks keep spawning, randomly.

Reloading the world or the game doesn't affect anything, chunks stay empty and I can build in those chunks, just like the 'normal' chunks.