Ambulances were outside the four-star Aqualux hotel in Bad Salzschlirf the whole day on Saturday, picking up guests and ferrying them to local hospitals.
The first guests started feeling ill on Friday night and by Saturday afternoon 30 of the 200 guests in the hotel were in hospital with the vomiting sickness.
The regional health ministry set up a crisis team to deal with the sick, and tests were started to try to determine whether a virus or a bacterial infection was to blame – or whether the guests were victims of food poisoning.
The state prosecutor in Fulda has also begun an investigation on the suspicion of negligent bodily harm having been committed by the hotel.
The hotel has been sealed off by police to prevent further cases of illness, while most of the remaining guests have gone home.