UK police on Tuesday questioned a 17-year-old suspect arrested after a "ferocious" knife attack which killed two children and critically injured eight others.
Flowers, teddy bears and tributes were left near the scene of Monday's stabbing spree at a Taylor Swift-themed dance class in Southport, near Liverpool, that also saw two adults and six children critically injured and three more children hurt.
Police chief Serena Kennedy said the two adults were trying to protect the children, aged between six and 11.
Swift on Tuesday said she was "completely in shock".
"The loss of life and innocence, and the horrendous trauma inflicted on everyone who was there, the families, and first responders. These were just little kids at a dance class. I am at a complete loss for how to ever convey my sympathies to these families," she said.
Residents of Southport, a small seaside town popular with visitors in the summer, were still coming to terms with the attack.
"I'm just still in total shock -- I just cannot believe that it happened so close to home," Leanne Hassan told reporters on Tuesday.
She had rushed to collect her daughter from a nearby nursery which was locked down after the attack.
Her daughter was safe, "but unfortunately that's not the reality for a lot of parents waking up today," she added.
Police chief Kennedy confirmed the attack was not being treated as terror-related and that the attacker's motivation was unclear.
Prime Minister Keir Starmer said the events were "just truly awful, the whole country is deeply shocked".
"It is almost impossible to imagine the grief," he added.
Interior minister Yvette Cooper visited Southport Tuesday to meet Kennedy and other officials, with an evening vigil to be held for the victims.
Starmer is likely to visit the community as well, Chancellor Rachel Reeves told Sky News.
The 17-year-old male arrested on suspicion of murder and attempted murder is from a neighbouring village called Banks and was born in the Welsh capital Cardiff, Merseyside Police said.
Witnesses told UK media the attacker was seen arriving at the scene in a taxi, and that he entered the venue wearing a mask.
Police said officers were called to the incident shortly before 1100 GMT on Monday, just minutes before the dance event was scheduled to end.
Armed officers detained the suspect nearby and seized a knife.
The suspect was in custody at a police station Tuesday and police said enquiries were ongoing "to establish the motive for this tragic incident".
Targeted attacks on children are extremely rare in the UK.
Monday's incident evoked memories of a school massacre in the Scottish town of Dunblane in 1996, which claimed the lives of 16 young pupils and their teacher in Britain's worst mass shooting.
The North West Ambulance Service said it treated 11 casualties with stab injuries, who were then taken by ambulance and helicopter to Alder Hey Children's Hospital and other hospitals in the area.
Local business owner Colin Parry, one of the people who called police, told the Press Association (PA) news agency that he believed several "young girls" had been stabbed.
A member of his staff also saw "about 10 kids go running past him, all bleeding, and one of them collapsed on the floor outside the neighbour next door," he recounted.
Bare Varathan, who owns a local shop, told PA he saw "seven to 10 kids" who were "injured, bleeding".
Other witnesses told UK media they heard screams, comparing the attack to a scene from a horror film.
King Charles III offered his "most heartfelt condolences, prayers and deepest sympathies" and called the incident "utterly horrific".
Prince William and his wife Katherine posted on X that "as parents, we cannot begin to imagine what the families, friends and loved ones of those killed and injured in Southport today are going through", calling it a "heinous attack".
