The students were in sports class at the Weißeritz high school reportedly suffered acute circulatory problems in the morning. Some 16 were treated in the hospital, while another 20 received ambulatory treatment.

Police in the Saxon community said at first they were baffled as to what could have affected the students so severely, speculating that there could have been a noxious substance circulating through the air.

But after air tests revealed no clues, and more students later collapsed in a neighbouring classroom, a district office spokeswoman said authorities had assumed the students had become infected with a norovirus.

By that time more than 70 students had reported symptoms of the highly-contagious bug, which causes sudden nausea, vomiting and diarrhoea.

The norovirus is the most common cause of gastroenteritis around the world and can be transmitted easily through contact with an infected person, by consuming contaminated food or water or by coming into contact with contaminated surfaces or objects.

Meanwhile in Hamburg on Tuesday, nine toddlers were rushed to a hospital on suspicion of food poisoning after eating tomato soup for lunch at their day care centre.

But according the first assessment by doctors they likely suffered an allergic reaction to too much flavour enhancer added to the dish by a catering service, a fire department spokesperson said.

Their symptoms included redness and swelling in the face.

DPA/DAPD/ka