A Bromley teenager died after he was punched, unprovoked, in the face following a friend's 16th birthday party, a court has heard.

17-year-old George Verrier died from a head injury on September 1 last year, after the party in Blenheim Road, Bromley.

Ben Hayes, 18, of Constable Mews, Bromley, is accused of manslaughter.

Max Kane, 17, says he left the party between midnight and 12.30am with a couple of friends.

He told the Old Bailey there had been no trouble at the party, although defence counsel Stephen Kamlish described it as "drug fuelled", with "ecstasy, cocaine, ketamine and cannabis" all on offer.

Mr Kane said there was an argument in the road outside between three people, which expanded to a group of 20.

He added the group moved up the road towards Southborough Lane.

He said: "Things moved up the road. I decided to follow because my friends were involved.

"There was an argument between Ben Hayes and George Verrier.

"George Verrier was trying to calm down Ben Hayes and tell him to stop because Ben Hayes was looking for a fight.

"He was shouting at him to calm down, he was telling him to leave it.

"Ben Hayes was very angry, he looked like he wanted to hit someone.

"He looked like he wanted to explode, to switch on someone.

"He (Hayes) punched him round the side of the face, in between the jaw and chin.

"The momentum with which he was hit span him round and it was like the life had been sucked out of his face.

"He hit him for no reason. George Verrier was no threat.

"He (George) just dropped. He was unconscious.

"I went up to him when he was on the floor. He was bleeding from his nose and mouth. I remember I thought to myself when he was on the floor he looked dead.

"About 10 seconds after that a police van came round the corner and as soon as Ben Hayes saw that police car he ran down the road.

"I have never seen someone run so fast in my life."

George came around shortly after and police officers gave him first aid. However they say he declined to be taken to hospital.

The London Ambulance Service did not attend.

George was found unconscious at his friend's house in nearby Ferndale at around 9.30am that morning.

The former Ravensbourne School pupil was taken to an east London hospital but was pronounced dead at 6.11pm that evening.

Hayes denies manslaughter.

The trial continues.