Man trapped under his car in NSW crash

A man is in a critical condition after he was thrown from his car and trapped beneath it in a crash in northern NSW.

Police say the 19-year-old man is in a critical but stable condition at the John Hunter Hospital with injuries including a punctured sternum and head injuries.

He lost control of his Toyota Camry at Upper Taylors Arm near Macksville at about 5pm Sunday and hit several trees.

He was helped by a witness but was trapped under his car for about an hour before he was freed and airlifted to hospital.

Police will interview the man when his condition improves and want to speak to anyone who saw the car before or during the accident.