VANCOUVER -- A spray park in Mission has been shut down after police say several children and their parents were exposed to an "unknown substance" that caused burning and skin redness.

Mounties say they were called to the Mission Leisure Centre on Grand Street around 12 p.m. Tuesday after receiving reports of an issue at the park. Mission Fire Rescue and BC Ambulance Service treated the patients on scene, and one person was taken to hospital. That patient has since been released.

The spray park was shut down immediately and has been closed by the District of Mission until further notice.

One parent told CTV News in an email she was at the park with her two daughters and saw many children treated by paramedics. In a Facebook post, another parent said several kids were crying and had burning eyes and mouths after someone let off pepper spray -- though authorities have not been able to confirm what the substance was yet.

Police have launched an investigation and are currently working with the district to determine where the substance came from. The district tested the water shortly after the incident but no "irregularities" were found, including with the chlorine levels.

"We are currently looking at all avenues, including engaging our Integrated Forensic Identification Services to identify the substance and its origin," Cpl. Nathan Berze said in a statement.

Anyone with information about the incident is asked to contact Mission RCMP at 604-826-7161 or Crime Stoppers at 1-800-222-8477.