TWENTYNINE PALMS (AP) — Marine Corps officials say five Marines accidentally exposed to a fire retardant gas during a training exercise at a Southern California base remain hospitalized.

Capt. Justin Smith said Friday the five were kept overnight for observation but were expected to be released soon. All had minor injuries. Smith did not elaborate, citing privacy concerns.

READ MORE: Tournament Of Roses To Name 2022 Rose Queen

Nearly two dozen Marines were treated for exposure to halon after an extinguishing system accidentally activated in an assault vehicle during an exercise Thursday at the Marine Corps Air Ground Combat Center in Twentynine Palms.

READ MORE: LA City Council Approves Nearly $40 Million Guaranteed Basic Income Pilot Program

Smith says officials are investigating the cause.

MORE NEWS: FDA Advisers Back Pfizer's COVID-19 Vaccine For Kids 5 To 11 Years Old

(Copyright 2015 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)