WWE Stage Catches Fire in Cincinnati

TMZ has learned ... the Cincinnati Fire Department raced to the US Bank Arena moments ago after a fire broke out on the stage at WWE rehearsals for last night "Monday Night Raw."

A rep for the WWE tells us the fire began due to a "minor incident involving the show's pyrotechnics" ... and as a precaution, the "limited number of people in the building during the incident were successfully evacuated."

The rep tells us no one was injured in the blaze ... and there was no major damage to the arena. We're told the fire marshal has since inspected the damage and gave the all-clear for WWE to proceed with tonight's event.