A class of 27 pupils and a teacher required medical attention after a suspected gas leak at a secondary school.
Two of the pupils collapsed and were taken to hospital while the rest were treated at the scene by ambulance staff.
North Yorkshire Police said emergency services were called to reports of several students collapsing at the Outwood Academy School on Clotherholme Road in Ripon at around 11.30pm.
The class complained of feeling sick and faint at Outwood Academy School.
A spokesman for North Yorkshire Fire and Rescue Service said specialist hazardous materials officers are at the school.
Police said the cause of the incident is still not clear but local councillor Bernard Bateman claims it may have been a gas leak.
He said: “The area has been completely cordoned off and there is a huge police presence. It looks like there has been a gas leak of some sort.
“There are five police cars and five fire engines outside the college-side of the school and the area has been evacuated.
“Police were checking underneath car bonnets.”
A spokeswoman for North Yorkshire police declined to comment on the gas leak claims.
In a statement police added: “Approximately 27 students have been affected who have displayed signs of sickness and feeling faint.
“Some have been attended to by paramedics at the scene and others have been taken to hospital.
“At this stage it is not known what has caused the students to fall ill and officers are working with the fire service to establish what has caused the incident.”
“North Yorkshire Fire and Rescue Service received a call at 12.21pm to reports of a number of pupils feeling unwell at the Outwood Academy in Ripon,” the spokesman added.
“Crews from Ripon and Boroughbridge are at the scene alongside hazardous materials specialist officers.
“A specialist detection, identification and monitoring team from West Yorkshire Fire and Rescue Service is also at the incident.
“A number of students have been affected who have displayed signs of sickness and feeling faint. Some have been attended to by paramedics at the scene and others have been taken to hospital.
“We are working with colleagues from North Yorkshire Police and Yorkshire Ambulance Service at this time to determine what has caused this occurrence.”