Three people have died and three more have been seriously injured after stabbings in a park in Reading, police confirmed.
A 25-year-old man from Reading has been arrested on suspicion of murder after being detained at the scene.
The attack happened at Forbury Gardens at about 19:00 BST where several people were stabbed.
Police are not currently treating the incident as terror-related, but counter terrorism officers were called.
Security sources have told the BBC a man arrested at the scene is thought to be Libyan.
Home affairs correspondent Daniel Sandford said he had been told the man had previously been in prison in the UK for a relatively minor conviction, not a terrorism offence.
One eyewitness told the BBC how he saw a man move between groups of people in the park trying to stab them and how the man ran towards him.
There were reports a police officer had “rugby tackled” the suspect to the ground, according to the Sunday Mirror.
Det Chf Supt Ian Hunter, from Thames Valley Police, said police were not looking for any other people in connection with the attack, adding that officers were “keeping an open mind as to the motivation for the incident”.
Police have asked anyone with mobile phone footage of the attack to come forward and people have been urged not to share videos and photos online “out of respect for the victims’ families”.
Thames Valley Police said the incident was not connected to an earlier Black Lives Matter (BLM) protest in the park.
About a dozen armed police officers carrying shields were later seen entering a block of flats in Basingstoke Road in Reading at about 23:00 BST.
BBC News Home Affairs correspondent Dominic Casciani, who was outside the block of flats, said he heard a loud bang at the scene.
Throughout Saturday evening, residents of the Basingstoke Road flats that were raided by the police stood – increasingly cold – on the footpath, watching on astonished as armed police entered their home.
The first officers arrived at 20:00 BST and secured the scene – apparently asking some residents to leave their flats or preventing others from returning.
Two specialist Incident Response Units from the ambulance service arrived – indicating that police were possibly taking additional precautions at the scene.
At 23:00 BST, more than a dozen armed officers, carrying shields entered the central block and climbed the stairs to the upper floors. At about 00:30 BST there was a loud bang that sounded like it came from inside one of the flats.
Shortly afterwards lots of the armed team left the scene. People here are shocked – but absolutely none the wiser as to what is going on.