Police are looking for witnesses after a man was hit by a vehicle in the ByWard Market early Sunday morning and suffered life-threatening head injuries.

It happened on George Street at Cumberland Street at about 4:45 a.m., police said, while the man was crossing the street.

The 27-year-old man was unconscious when paramedics arrived at the scene. He was taken to The Ottawa Hospital's Civic campus trauma unit in critical condition, and was later upgraded to serious condition.

No other details were immediately available.

George Street was closed for several hours but has since reopened.

Anyone with information is asked to call the collisions unit at 613-236-1222, ext. 2481.