Honolulu police are investigating a solo motorcycle crash that occurred Saturday night, sending a 42-year-old man to the hospital in critical condition.

Police said at about 8:05 p.m. Saturday, the motorcyclist was heading westbound on Kalanianaole Highway when he lost control just past the Makapuu Lighthouse Trail entrance and collided with the guardrail of the eastbound lane.

Police said the motorcyclist was ejected onto the roadway and taken by Emergency Medical Services to a hospital in critical condition.

He was not wearing a helmet at the time of the collision.

EMS said the man suffered injuries to the left side of his extremities and to his head.

Police said it is unknown if speed, drugs, or alcohol are contributing factors in the collision at this time.

The investigation is ongoing.