One man was killed and the two others were seriously injured in a trio of motorcycle accidents that occurred around Hawaii island Monday morning within a three-hour time span.

The fatality occurred about 7:26 a.m. after a Honda sedan traveling on Highway 19 near Hau Street north of Hilo made a U-turn in front of the motorcycle, which struck the sedan broadside, Hawaii police said.

The operator was not wearing a helmet and was taken to Hilo Medical Center, where he was pronounced dead at about 8:14 a.m. His identity remains unknown, police said.

The 63-year-old female driver of the sedan was treated for minor head injuries.

The other accidents occurred in North Kona at 7:42 a.m. and Hilo at 10:23 a.m. Both motorcyclists — a 57-year-old Kailua-Kona man and a 28-year-old Hilo man — are in critical condition at area hospitals.