Street vendor disappearances

Last week, I was talking to a coworker who lives in the same complex as me how the street vendors had all disappeared. Today I came off the metro to see no street vendors, but lots of people standing around. One of the street vendors had her cooked goods and cooking paraphernalia on the ground, but no cart. Then suddenly a horde of policemen descended on her and took some of her paraphernalia.

In the picture above, you can see steam rising off the "sweet potato and corn cart" which all the policemen are gathered around (waiting for it to cool?). And on the back of the truck, you can see the "unremarkable omelette cart" waiting to be taken away. I wonder why the police do this.. street food is one of the many enjoyable things that make Shanghai and I imagine China in general a great place to live.