Rotherham College's Dinnington Campus was closed earlier after a small group of students in one of the college's workshops reported feeling unwell.
Police officers, firefighters and paramedics all attended the scene and other students were asked to remain in their classrooms.
College in Rotherham closed after students fell ill in classroom The cordon has now been lifted and those students who have not been released by the emergency services are being monitored as a precaution.
A South Yorkshire Fire and Rescue service spokesperson said: "The incident at Rotherham College is now being scaled down, the students have been assessed and are now being released, the cause of the symptoms have been investigated but remain unknown."
A spokesperson for Rotherham College said: "Following the earlier incident: Four students who were assessed by the emergency services have now been released by them. Five are remaining sat with the emergency services, who are monitoring them as a precaution.
Emergency services called to incident at Rotherham college "In the building, classes are continuing, though mobility around the site continues to be restricted as a precautionary measure. There is not felt to be any risk to anyone else.
"Emergency services are investigating what was the cause of this incident, which was restricted to one workshop outside of the main building.
"We will update as soon as possible when we have more information and the campus is back to normal."