More than 30 people were hospitalized at a school in Kingston, Massachusetts, Friday, after a teacher detected a nauseating odor, fire officials said.

It remains unclear what caused the hazardous materials situation at Silver Lake Regional High School at 260 Pembroke St, but all-clear was given after a thorough search, officials said.

"It could be something that the student brought with them, that's a possibility. It could be an irritant," Kingston fire Chief Mark R. Douglass.

State fire officials said the initial call came in around 10 a.m. for an odor in a classroom.

A staff member reported feeling nauseous and a strong odor coming out of a classroom, according to a message sent to parents. Police and fire officials were immediately notified.

"It was really heavy in your lungs, like you could feel it in there," said junior Jason Martin of the noxious odor.

The 1,200 students in the school were evacuated to the school gym, with anyone not feeling well taken to three area hospitals. There were complaints of dizziness and throat irritation, Douglass said.

The number of people hospitalized rose from one teacher and several students to 30 people to, finally, 34 people taken to three area hospitals and put under quarantine in case there were contamination issues, according to Douglass.

Hazmat officials recommended that the school's HVAC system be shut down and the school evacuated while the situation is assessed, state fire officials said.

Professional cleaning crews were giving the school a thorough cleaning Friday evening so it's ready for classes again Monday, Douglass said.

"Relax, we've got it under control," Douglass said. "They can rest easy."