A Canberra man celebrating his 18th birthday went for a drive to buy more alcohol and crashed his car into a tree, causing his friend to fly into the windscreen and "sever" an artery in his neck, court documents say.

Kade McKelvie, 18, pleaded guilty in the ACT Magistrates Court last week to culpable driving causing grievous bodily harm.

A police statement of facts tendered to court said the Greenway man had spent the night of November 18, 2016 drinking in Civic before going home with his friends about 3am to continue drinking.

At 7am he said he was going to the shops to buy more alcohol.

His friends, one who later described McKelvie as heavily intoxicated, warned him against driving and hid his keys, but shortly after they heard the car start, police said.

McKelvie had bought the Holden Barina three weeks earlier for $200. It was unregistered, he was unlicensed and he hadn't yet transferred the car registration to his name. Its plates also belonged to another car.

His two friends came running outside on hearing the engine and after failing to convince McKelvie not to drive, they got into the front passenger and back seat to make sure he drove safely.

But when McKelvie pulled out into Barr Smith Avenue he drove on the wrong side of the road before he veered back onto the right side, mounted the curb and crashed into a tree.

The crash at the intersection of Barr Smith Avenue and Don Dunstan Drive in Greenway was less than 500 metres from his home.

The man in the back seat - who police say may or may not have been wearing a seatbelt - had flown into the windscreen and his head punched a hole in the glass. He sliced an artery in his neck, causing blood to cover his face and spray everywhere, police said. He suffered a laceration from his lip to beneath his chin and lost a tooth.

Nearby residents saved his life by wrapping a towel around the injured man's neck, and he was taken to hospital for emergency surgery.

The man in the passenger seat was knocked unconscious.

McKelvie fled the scene. With help from a member of the public who identified the driver, officers found McKelvie lying face down on his bed with a blood spattered singlet lying on the floor in his room.

On Friday McKelvie pleaded guilty to culpable driving causing grievous bodily harm, driving unlicensed, driving an unregistered and uninsured car and failing to stop or give assistance.

His defence is still considering a further charge of affray.

The case is due to return to court for sentencing on July 10.