A 17-year-old girl has sustained "life-threatening" injuries after a car carrying four people hit a tree.
The silver Ford Focus crashed on the B4507 at Kingston Lisle near Wantage, Oxfordshire, at about 01:00 BST.
The girl was taken to hospital along with another back-seat passenger - an 18-year-old man whose injuries are described as "life-changing".
The driver, a 27-year-old man, and another 17-year-old girl riding in the front were not seriously hurt.
Police said no-one had been arrested.
They have appealed for witnesses and dash-cam footage of the vehicle being driven before the crash.