An overseas rider sustained critical injuries following a serious accident in the Lightweight/Ultra Lightweight race during the Dundrod 150 meeting at the Metzeler Ulster Grand Prix on Thursday.
The event was delayed for around an hour as a result of the crash, which happened at the high-speed Rock Bends section of the 7.4-mile circuit.
The competitor involved was transferred to the Royal Victoria Hospital in Belfast for treatment.
Prominent English rider Danny Webb was also involved in a crash earlier in the day, sustaining suspected fractures, although his condition is not believed to be life-threatening.
Webb, from Kent - a former world championship Grand Prix rider - came off at Joey’s Windmill during practice for the Ulster Grand Prix Supersport class.
Practice was restarted after a delay, but Clerk of the Course Noel Johnston scrapped the session after receiving reports that some riders had ignored waved yellow flags when Russ Mountford slid off at the Lindsay Hairpin.