Burglars broke into a school kitchen and stole all its food, including four full large freezers.
The raid at Gosfield School in Essex happened overnight on Friday.
It said it would no longer be able to feed the children of key workers, or its staff, because of the theft.
Among the items taken were four commercial freezers full of food, all the dry foods in the kitchen and the contents of the catering refrigerators, said the school.
It added that staff at the school near Halstead were "incredibly saddened".
Essex Police said it was investigating the burglary.
It happened after schools closed on government orders due to the coronavirus outbreak.
On its Facebook page, the school explained it would now be unable to feed the children of key workers who are still attending and staff who have agreed to run a "skeleton operation".
It said staff had been into the village to purchase food "but with restrictions on what they are allowed to purchase this is not straightforward".
Supermarkets have started to restrict sales of essential food and household items as a result of coronavirus stockpiling.
The school has asked children of key workers, as identified by the government, to take a packed lunch to school.
More than than 1,600 people have commented on the Facebook post to express their "disgust".
One person wrote: "What a horrible thing to happen, so sorry for the school."
Another said: "Unbelievable... Whatever happened to 'pulling together'."