FRESNO, Calif. (AP) — Authorities in central California say seven inmates from the Fresno County Jail were rushed to the hospital overnight after being exposed to an unknown substance.

Tony Botti, a spokesperson for the Fresno County Sheriff’s Office, told the Fresno Bee Wednesday that several ambulances were called to the jail around 10:30 p.m. on Tuesday after staff members noticed the inmates seemed ill.

A hazardous materials cleanup crew was sent to the jail. Authorities have not said what kind of substance the inmates were exposed to. Botti says the investigation is ongoing. He says all the inmates are now doing OK and are expected to recover.