CLINTON — A 20-year-old man remained in serious condition Monday after crashing his moped a day earlier in Clinton, police said Monday.

The crash occurred at about 3:45 p.m. Sunday when the man flipped his moped after veering off the road and into a ditch near 510 Hill Road, according to Mike Conners, public information officer for the Clinton Police Department.

The man was not wearing a helmet when he crashed and was the only person involved in the crash.

While the crash’s cause remained unknown Monday, Conners said speed did not appear to have been a factor.

“While the cause of the crash is still under active investigation, initial assessments suggest the possibility of a serious medical event suffered by the male operator,” Conners wrote in a statement to the news media.

The operator of the moped was first taken to MaineGeneral Medical Center’s Thayer Center for Health at 149 North St. in Waterville. He was then taken by a LifeFlight of Maine helicopter to Northern Light Eastern Maine Medical Center in Bangor.

“We extend our thoughts and prayers to the injured individual and his family during this difficult time,” Conners said.

Clinton police are leading the investigation into the crash. They ask that anyone with information call 207-426-9192.