In Shanghai, if a person is infected with covid-19, the entire community is closed for 14 days. If you were in close contact with that infected person, the entire building you lived in would be sealed off.
Therefore, many communities in Shanghai are currently blocked, which causes everyone to stock up on food because everyone is worried that their communities will be blocked.
Many of my friends' homes are also short of food. A few days ago, a friend's home had no vegetables and meat, and only noodles were left. There were also friends who thanked the people who brought them food.
Fortunately, food shortages are temporary, mainly due to short-term supply shortages caused by people rushing to stock up. It will be fine in two or three days.
Although I believe that there is no shortage of food in Shanghai, I also went to the supermarket to buy a lot of food and filled the refrigerator in order to feel safe.