MADISON, NJ (PIX11) — A dozen children were sickened by exposure to a higher than normal concentration of liquid chlorine while they were in the pool at a New Jersey soccer program on Monday, officials said.

Emergency responders headed to the pool area of Drew University after a 911 call around 12:12 p.m. The kids, who are taking part in a summer soccer program for children ages 10-17, suffered from shortness of breath, difficulty speaking between breaths, nausea and general airway issues, Morris County Office of Emergency Management Director Jeffrey Paul said.

The children were assessed and several of them needed to be taken via ambulance to a hospital for further treatment, Paul said. Officials have not yet said how the chlorine incident started.