A man in his 50s suffered life-threatening injuries after he was struck by a truck in downtown Calgary  earlyMonday morning.

Police said in a news release that officers were called to the intersection of Ninth Avenue S.E. and Third Street S.E. for reports of a collision involving a pedestrian around 5:30 a.m.

Investigators believe a 2004 GMC Sierra travelling east on Ninth Avenue S.E. struck the man as he attempted to cross the road without using a crosswalk.

The pedestrian is believed to have been struck by the driver-side corner of the truck, resulting in life-threatening injuries, police say. The man remains in hospital in serious condition.

The driver of the truck was not hurt and initially continued east from the collision scene, but “quickly returned,” police said.

Impairment and excessive speed are not believed to be factors in the collision, however the investigation is ongoing.

Anyone who witnessed the collision or may have dashcam footage from the area at the time of the incident is asked to contact police.