Very very scary. Here is what they are - click for more images.
A sinkhole is a natural depression caused by the removal of underground soil by water. Usually, it happens when the substrate is formed by limestone, carbonate rock, salt beds or any other rock that is easily eroded by water streams. The process could be slow, but sometimes the land just cracks open without notice. In this case, it happened suddenly, swallowing an entire factory (luckily no one was inside!). The cause: Massive underground water torrents created by tropical storm Agatha.