A cyclist is in critical condition with serious head injuries after colliding with a dog while riding in Uxbridge, northeast of Toronto.

Durham Region police say the 48-year-old Pickering man was not wearing a helmet when he was thrown from his bike Monday afternoon.

Police say two dogs ran out onto the roadway from a nearby residence and the cyclist hit one of them, a shepherd mix.

A passing motorist stopped to help and emergency services were called.

The cyclist was taken to hospital in Newmarket and then transferred to Sunnybrook Health Sciences Centre in Toronto where he remains in critical condition.

One of the dogs was injured and taken to the vet by its owner, while the other dog was not hurt.