A woman was found beheaded in a back garden in north London, according to British media reports, but police said the attack was not linked to terrorism.
Police discovered the body in the suburb of Edmonton after being alerted at midday by local residents who said a man with a knife was attacking a cat or dog.
They would not confirm reports she had been beheaded, nor some media descriptions that the act was carried out with a machete.
A 25-year-old man has been arrested on suspicion of murder and is in custody, they said.
Eyewitness Freda Odame, 30, told The Telegraph that she saw a man in his mid 20s as she looked through the window of her home.
“Someone was shouting and the door was banging. I could hear the screaming but I could not hear what he was saying,” she said.
“I could see that he had a big curved knife, about the size of an arm’s length and he was crouching as if frantically searching for something.
“He had a crazed look in his eyes so I closed my curtains because I was scared. My next door neighbour was in his garden but did not seem to realise anything was going on.
“I have seen him around here all the time, I think he lives on the road, He has a grey car and I think he lives with his family.
“I was just so very scared. Five minutes after I heard him screaming the police knocked on my door and told me I had to get out.”
Police evacuated residents from their homes as the man ran through a row of back gardens.
"At first there were two police cars, then all of a sudden there were 20," one witness, 19-year-old Ahmed Yusuf, said.
"The police said to drop everything ... They said there's a guy jumping over gardens."
Local resident Lauren Perkins told the Enfield Independent:
"I was walking down the road when I saw a man with a big knife walking down the street.
"Then I saw some police come down and they told me to get off the road. I just can't believe something like that would happen. It's just so shocking.
Detective Chief Inspector John Sandlin of Scotland Yard said they were not looking for anyone else over the incident.
"This was a highly visible attack in broad daylight on a residential street," he added.
"Whilst it is too early to speculate on what the motive behind this attack was, I am confident based on the information currently available to me that it is not terrorist-related."