The Riverside County Fire Department said there were a total of at least 25 patients, with at least five in critical condition and nine in moderate condition. One bus was requested to help transport patients with minor injuries.
The source of the illness is still being investigated.
Nine fire engines were on the scene, as well as a hazmat crew and environmental investigators as people reported having symptoms of nausea and shortness of breath.
Riverside County firefighters responded to the scene at the 31100 block of San Timoteo Canyon Road after reports came in at about 8 p.m.
Nine ground ambulances also arrived at the scene.