The knife attack occurred in Southport, a seaside town in Merseyside, which is north of Liverpool, Merseyside Police said.
Authorities were called to a property on Hart Street at 11:50 a.m. (6:50 a.m. ET) on reports of a stabbing.
In an update later Monday, police said that in total two children died and nine others were injured — six of them critically. Two adults were also critically injured as they tried to defend the children, police said.
The children were attending a Taylor Swift-themed event at a dance school when the offender — described as a 17-year-old male from Banks, a nearby village — walked in armed with a knife and "started to attack inside the children," Merseyside Police Chief Constable Serena Kennedy said at a news conference.
"We believe that the adults who were injured were bravely trying to protect the children who were being attacked," Kennedy said.
"As a mum and a nana, I can’t begin to imagine the pain and suffering that the families of the victims are going through at this moment and time, and I wish to send my heartfelt condolences to them," she added.
The teenage suspect was arrested on suspicion of murder and attempted murder. He remains in custody and will be questioned.
Police earlier said that a knife was seized, as well.
Police said in a statement that “enquiries are ongoing to establish the motive for this tragic incident.” Officials said that the attack is not being treated as terrorist-related and that no one else is believed to be connected. There is no wider threat to the public, they said.
Police ask witnesses or anyone with information about the incident to come forward.
Colin Parry, who owns the business next to the community center that was hosting the children’s event, said one of his colleagues called him and told him to get outside, where he witnessed utter horror.
“It was definitely intentional. It wasn’t once. It was several times he stabbed these kids. The man is crazy,” he told Sky News.
MNA/PR