OPP has confirmed one person has died following a single-vehicle roll-over on Highway 11 through Gravenhurst on Thursday.

ORNGE tells CTV News two other people, a man and woman, were transported by air ambulances to Toronto trauma centres in critical condition.

Muskoka paramedics say they rushed a fourth person with serious injuries to a Bracebridge hospital.

Police say the NB lanes will remain closed for several hours, but southbound is now moving.

Gravenhurst collision