The Prince and Princess of Wales have sent "love, thoughts and prayers" to the victims of the "heinous" attack in Southport.
In a heartfelt message shared on social media on Monday evening, Prince William and Kate said: "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."
The couple added: "Thank you also to the emergency responders who, despite being met with the most horrific scenes, demonstrated compassion and professionalism when your community needed you most."
The message was signed off personally with their initials "W & C".
Meanwhile, the King released his own message, writing: "My wife and I have been profoundly shocked to hear of the utterly horrific incident in Southport today.
"We send our most heartfelt condolences, prayers and deepest sympathies to the families and loved ones of those who have so tragically lost their lives, and to all those affected by this truly appalling attack. Charles R."
Two children have died and nine have been injured, including six who are in a critical condition, following the stabbings in Southport, Merseyside Police Chief Constable Serena Kennedy said. Two adults are also in a critical condition.
Constable Kennedy said a 17-year-old male from Banks, Lancashire had been arrested on suspicion of murder and attempted murder over the "ferocious attack" at a Taylor Swift event at a dance school in Southport.
In a statement on X earlier today, Prime Minister Keir Starmer said: "Horrendous and deeply shocking news emerging from Southport. My thoughts are with all those affected. I would like to thank the police and emergency services for their swift response. I am being kept updated as the situation develops."
Statement from Chief Constable Serena Kennedy
The statement released by Constable Kennedy on Monday read in part: "A 17-year-old male from Banks in Lancashire, who was born in Cardiff, has been arrested on suspicion of murder and attempted murder and has been taken to a police station where he will be interviewed by detectives
"My officers were called to reports of a stabbing at 11.47am at an address Southport. When they arrived they were shocked to find that multiple people, many of whom were children, had been subjected to a ferocious attack and had suffered serious injuries.
"It is understood that the children were attending a Taylor Swift event at a dance school when the offender, who was armed with a knife, walked into the premises and started to attack those inside. We believe that the adults who were injured were trying to protect the children at the time they were attacked.
"As a mum of two daughters, and the nanna of a five-year-old granddaughter, I cannot begin to imagine the pain and suffering the families of the victims are currently going through and I want to send them our heartfelt condolences and sympathies.
"Our specialist Family Liaison Officers are providing support to the families at this terrible time."