BERLIN—At least 84 people have been exposed to a suspected irritant gas at a high school in southwestern Germany, according to German news agency dpa.

Both students and teachers experienced mostly slight health effects at the school in the town of Singen, dpa said. Three students and a teacher, however, had to be taken to the hospital after experiencing severe respiratory problems.

The school was evacuated and police cordoned off the area Wednesday. It was not immediately clear if the incident involved a leak or a spill.

During the fourth lesson, several students suddenly complained of respiratory problems and teachers began evacuating the building and making emergency calls. Symptom-free students were taken to a nearby church, where they were picked up by their parents, dpa reported.

Irritant gases include ammonia, chlorine, hydrogen chloride and sulfur dioxide. Inhaling their vapors can cause respiratory problems.