A man was beheaded in a frenzied and prolonged axe attack in a London street today.

The axeman, smartly-dressed and in his thirties, felled his victim with one blow and then struck repeatedly "as if he was chopping wood".

The assault lasted several minutes near the Hampstead Theatre in Belsize Park. The attacker ignored his victim's screams and the pleas of two women passers-by and workmen. He stopped when police arrived. He then put down the axe near the body. He was described as looking "emotionless and cool" throughout.

When asked why he had done it, he told officers: "It's complicated. It's private."

Mothers on the morning school run were among those who saw the killing in Eton Avenue.

Police said the victim was in his sixties and is thought to have lived nearby.

Officers do not think it was a random attack and understand that the men knew each other.

A neighbour said there had been a series of domestic rows at a nearby address.

A scaffolder working nearby saw a man carrying an axe in one hand above his head as he ran towards his victim. The men were seen to exchange a few words.

Seconds later the axeman struck the first of a series of heavy blows which continued when the victim lay slumped on the pavement in a pool of blood.

The workman said: "It was unremitting. The man with the axe ran at his victim and just laid into him.

"He brought it down on his head and floored him. The victim had tried to defend himself with his arms and I heard him shout something. But it was hopeless.

"Within seconds he was on the floor and his head had been split open. There was blood pouring from his head and spilling onto the pavement. It was horrific."

Avelina Rodrigues, 48, said the attacker ignored her pleas to stop as he brought blow after blow down upon his victim, leaving the body badly mutilated.

She said: "I heard the first thuds of the axe as it hit the man's head. I thought it was the sound of a child being hit by a car.

"I ran to the front of the house and could see a man, smartly dressed, tall and thin, with the axe in his hand.

"The axeman saw me but he just ignored me. He hacked his victim's head, cutting it as if it was a block of wood for a fire. His victim was unconscious on the ground, but he kept bringing his axe down on him.

"I begged him to stop and he just looked at me without emotion. There was no anger in his face, he did not seem crazy. He was just coolly finishing off his victim. He wanted to destroy him. ."

Another woman passing in a car stopped and pleaded with the man to stop his attack. He also ignored pleas from builders working nearby. Police arrested a man at the scene and he is being held for questioning at Holborn police station.

Eton Avenue is known as one the most exclusive streets in north London with a host of multi-million-pound properties. Belsize Park is also the home to a host of celebrities, including Jude Law, his estranged wife, Sadie Frost, Gwyneth Paltrow and her rock star husband, Chris Martin.