Three people are feared dead and several have been taken to hospital after being stabbed in a serious incident in a park in Reading.
Police were called to Forbury Gardens at about 19:00 BST following reports of a stabbing – but neither the number of injured or fatalities have been officially confirmed by police.
Thames Valley Police said a man was arrested at the scene and is now in custody.
Security sources have told the BBC the man arrested at the scene is thought to be Libyan.
Counter terrorism officers are at the scene.
A Black Lives Matter protest was held in the area earlier, but Thames Valley Police and BLM organisers have said the incident was unrelated.
What did witnesses see?
BBC correspondent Helena Wilkinson said one eyewitness told her that he saw a man move from group to group stabbing people, and then quickly leave the park.
There were reports that a police officer “rugby tackled” a suspect to the ground, according to the Sunday Mirror.
What has the reaction been?
Prime Minister Boris Johnson said his “thoughts are with all of those affected by the appalling incident in Reading”.
“My thanks to the emergency services on the scene,” he added.
Home Secretary Priti Patel tweeted to say she was “deeply concerned” at the incident.
She said: “My thoughts are with everyone involved, including police and emergency responders at the scene.”
Labour leader Sir Keir Starmer said the stabbing was “very concerning”.