Ottawa police are investigating after pepper spray was released on an OC Transpo bus in east Ottawa Monday afternoon, sending at least four people to hospital.

Emergency crews were called around 1:30 p.m. to a bus that had pulled over on a Montreal Road off ramp from Highway 174.

Ottawa paramedics said they assessed six people for minor respiratory issues after the incident.

Four people were taken to hospital to be treated for minor respiratory issues.

Ottawa police said around 2:45 p.m. officers on the scene hadn't taken anyone into custody as they were still working to figure out who set off the spray and why.