A mass stabbing in a Reading park has killed three people and left three more seriously injured but is not currently being treated as a terror attack, police say.
A 25-year-old man from the Berkshire town has been arrested on suspicion of murder after the incident in Forbury Gardens at about 7pm on Saturday.
The alleged knifeman was "rugby tackled" to the ground by a hero police officer, a source said.
Heavily-armed and masked police officers were later seen at a block of flats in Reading after Saturday evening's attack, with a controlled explosion heard from inside by onlookers as residents were evacuated.
A shaken witness told Mirror Online he saw blood spurting and victims dropping "like a weight" as a man appeared to be "tapping them on the head" at random.
Another witness said the knifeman "shouted some unintelligible words" and stabbed victims in the neck and under their arms as the horrific mass stabbing unfolded.
Extremely graphic video on social media shows at least four people covered in blood while witnesses and police officers performed CPR on victims who appeared to be motionless.
It was initially reported that the attack was terror-related, but police have since said they are not treating it as a terrorism incident although they are keeping an open mind.
It is a chaotic and distressing scene with one-person shouting "He's still breathing", another asking for a defibrillator, officers running around the unsecured scene, and police sirens blaring in the background.
A source told the Sunday Mirror that a hero police officer saw a suspect running away with a knife and "rugby tackled him to the ground".
Prime Minister Boris Johnson said his thoughts were with those affected by the "appalling" incident, and Home Secretary Priti Patel said she was "deeply concerned" following the incident. It is understood Ms Patel is being kept updated on the situation.
Two people with stab wounds were rushed to the Royal Berkshire Hospital and were being treated in the emergency department. Two air ambulances landed at the scene and armed officers and a police helicopter were among the large presence.
A source told the Sunday Mirror: “A man pulled a knife and started attacking people at random in Reading, near the Crown Court. It is thought there was one attacker.
"It appeared the attack was stopped when a lone sergeant, who responded when the alarm was raised, ran to the scene, saw the attacker running away with a knife and rugby tackled him to the ground.”
Dan, a 26-year-old local, said he was drinking wine in the park with two friends when he noticed a commotion about 20 metres away.
He described how he and his friends had chosen a spot to sit and enjoy the sunshine when he saw a man approach a group "just in a circle chatting".
The man drew his attention because he appeared to be racing around the group "tapping them on the head".
Reflecting on the disturbing moment he realised it was an attack, Dan said: "I thought they were playing duck goose and thought someone had been sick, we realised it was blood spraying out."
He and his two friends sprang up and began running as they saw the attacker move toward another group in what he thought was a random attack.
Dan said he saw the man take a blow to a woman's neck- but couldn't be sure if he was using a knife as he and his friends never got a close look at the weapon.
The woman "dropped like a weight," Dan said.
Four people were on the ground and "immobile", and there may have been additional victims, he said.
He added: "I saw a man with his face bleeding but stood up. When the first 2 people were stabbed the group stood up, and two of the people who dropped to the ground were stood up."
Dan said it all happened so quickly, the crowds in the busy park hadn't noticed as they ran by.
He added: "It was strange - not like you see in films, there was no screaming.
"We were running by people dancing in groups - they hadn't seen what happened."
He saw the attacker run toward Reading Station, so he and his friends ran in the opposite direction.
A second witness, Lawrence Wort, was sitting close to the group in the park when the attack unfolded, and said it appeared to be "completely random".
Mr Wort, a 20-year-old personal trainer from Chippenham, said: "The park was pretty full, a lot of people sat around drinking with friends when one lone person walked through."
"[He] suddenly shouted some unintelligible words and went round a large group - of around 10 - trying to stab them.
"He stabbed three of them severely in the neck, and under the arms and then turned and started running towards me when we turned and started running."
"When he realised that he couldn’t catch us he tried to stab another group sat down."
One of the victims was stabbed in the back of the neck, and when the attacker realised everyone was starting to run, he ran out of the park, said Mr Wort.
Another witness, who asked not to be named, told Mirror Online she saw the emergency services performing CPR on at least three people.
She said: "My husband and I were walking back from Tesco after a grocery run, we always walk there.
"We take a break halfway at Forbury Gardens. I sat with my bags, drank water. I heard some children scream and cry, and assumed they were cranky.
"I was pointing to a mound and told my husband it would be perfect for a picnic spot.
"That's when I heard sirens. We saw emergency services perform CPR.
"We rushed outside the gardens and continued walking onto Friar Street."
The woman said she was terrified by what she witnessed and was feeling "very shaken" back at home.
Detective Chief Superintendent Ian Hunter, Head of Crime, said: “The Thames Valley Police Major Crime Unit has launched a murder investigation following this incident.
“We have made one arrest and at this stage we are not looking for any other people in connection with this incident. There is no intelligence to suggest that there is any further danger to the public, however we urge people to remain vigilant and report anything suspicious by calling police.
“This is not currently being treated as a terrorism incident, however officers are keeping an open mind as to the motivation for the incident and are being supported by colleagues from Counter Terrorism Policing South East.
“There have been some reports that this incident was linked to the Black Lives Matter protest which took place in Reading earlier this afternoon. I can confirm that this incident is not connected. It occurred around three hours after the protest had concluded.
“We are also aware that the incident was captured on mobile phones and would like to hear from anyone who has video footage. Out of respect for those deceased and injured, along with their loved ones, please do not circulate this footage on social media – this will be incredibly distressing.
“Police cordons continue to be in place and are likely to be for some time as we work to establish the circumstances of what has happened. You will also see an increased police presence in the area as we continue to make enquires.
“I would urge the public to avoid the area at this time and thank the community for their patience. We will let you know as soon as the area is back open.
“The thoughts of everyone at Thames Valley Police are with those who have been affected by this tragic incident and I understand the concern that this will have caused amongst the community. Please be assured that safety of the public is our primary concern and we will do all that we can to investigate this incident robustly and bring those responsible to justice.”
South Central Ambulance Service NHS Foundation Trust said in a statement: "We were assessing and treating a number of casualties who had sustained injuries as a result of the incident. Thank you to all those people who stopped and helped those who were injured as a result of this situation."
Police sealed off a large area and local councillors urged people to stay away from the active scene.