The injured Mississauga boy was loaded into an ambulance early morning Wednesday. The injured Mississauga boy was loaded into an ambulance early morning Wednesday. (CBC)

A three-year-old Mississauga boy was seriously injured after he left his home in the middle of the night and was struck by a car, police say.

It's believed the boy left through the front door of his family's townhouse on Britannia Road near Glen Erin Road around 1 a.m. Wednesday, while his parents slept.

Police said he put on his father's running shoes, squeezed through a break in the fence and wandered onto the road.

Investigators measured skid marks presumed to have come from a vehicle that swerved before hitting the child.

The boy was taken to Mississauga's Credit Valley Hospital before being airlifted to the Hospital for Sick Children in Toronto.

A 48-year-old Mississauga man was later arrested, but has not been charged in the incident, Peel Regional Police said.