One person is in a Hamilton hospital in critical condition following what police are calling an attempted murder on Highway 401.

The exact sequence of events is not known, but appears to have begun sometime before 5:30 a.m. Wednesday on the westbound 401 near the Cambridge service centre.

OPP say they believe one person fell out of a vehicle in that area, suffering serious injuries, but they’re not sure if that person jumped out of the vehicle or was pushed out.

“We don’t know the sequence of events that led up to that point,” OPP Sgt. David Woodford tells CTV News.

“Apparently it occurred on the highway, where we’re finding evidence.”

After the incident near the service centre, a vehicle began driving east in the westbound lanes, prompting other motorists to notify police.

OPP responded and stopped the vehicle in Puslinch Township, near the exit for Highway 6 North.

As an officer approached the small Toyota vehicle, it allegedly attempted to leave the scene – hitting a marked OPP cruiser as it did so.

The driver was then arrested and taken into custody without suffering injuries.

Officers retraced the vehicle’s drive down the highway, where they found the injured person along the highway.

Information on the identities of the people involved was not immediately available.

Two westbound lanes of the highway were closed for most of the day for police investigation, with the entire westbound stretch between Townline Road and Highway 6 North for three hours Wednesday afternoon.

All lanes reopened shortly after 4 p.m.