A 43 year old Greymouth woman and her 15 year old son died as a result of a crash on Taylorville Road about 11am today.
A pre-school boy who was also in the vehicle has been taken to Grey Base Hospital.
Highway Patrol Sergeant Dave Cross said the vehicle was travelling down hill into a bend in wet conditions. He said the car had gone over bank and landed upside down in a creek.
A serious crash investigation is under way and Police are in the process of notifying next of kin.