Dozens of English school students have fallen ill in a crowd during a ceremony commemorating Remembrance Day, and authorities are at a loss to explain what caused the incident.

As many as 40 children at Outwood Academy in Ripon in North Yorkshire were treated by emergency services after a number of children started fainting during the ceremony, although what brought about the phenomenon remains unclear.

In total, four children fainted during the incident, but dozens of others reported feeling unwell, causing considerable concern for their parents in addition to teachers and emergency responders on the scene.

"When the first boy was sick, we thought it was a one-off but then there was a big slap on the floor and someone had fainted," said one student, who asked not to be named, as reported by AFP.

"After that it was a bit of a domino effect – another three or four collapsed and then people started leaving the hall to get fresh air … they ushered us out quickly and a couple of girls had panic attacks."

Only one student was injured in the incident, and was treated for a bumped head at a local medical centre. Most puzzling is why the mass illness happened in the first place, after an assessment of the hall in which the faintings occurred revealed nothing untoward.

"Investigations have been carried out by the specialist detection, identification and monitoring team from West Yorkshire Fire and Rescue Service along with the specialist hazardous material officers from North Yorkshire Fire and Rescue Service and no hazardous chemicals or gases have been found within the school," said a spokeswoman from the North Yorkshire Fire and Rescue Service.

The best guess is that some of the children may have overheated in the hall, leading the initial fainting, which created a knock-on panic effect that spread throughout the crowd. Similar incidents have happened before, although they are extremely rare.

"We are of the view the children just fainted and there was a ripple effect throughout the school," Dave Winspear of the North Yorkshire fire service told AFP. "More children felt anxiety and started to feel concerned and the thing has escalated."

While it seems unlikely that a more detailed level of explanation will be provided for the incident, all concerned are grateful that at least nobody was seriously harmed in the puzzling episode.

"In cases like this where we have such a high number of people fall ill in such a small environment, it is our responsibility to take this extremely seriously and ensure a multi-agency response to fully investigate the circumstances," said superintendent Nick Hunter at North Yorkshire Police. "Thankfully in this case, it was nothing serious and the incident has been brought to a safe conclusion."