Two children were killed and nine more were injured in what police described as a “ferocious” stabbing attack in northwest England Monday morning during a Taylor Swift-themed dance event. A 17-year-old male was later arrested in connection with the violence.

The knife attack unfolded 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 update later Monday, police said that in total two children died in the stabbing attack, another nine were injured — six critically. Two adults were also critically injured in the incident 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,” Chief Constable Serena Kennedy of Merseyside Police said at a press 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 teen offender has been arrested on suspicion of murder and attempted murder. He remains in custody and will be questioned regarding the incident. 

Police earlier said that a knife was seized as well.

“Enquiries are ongoing to establish the motive for this tragic incident,” police said. Officials say the attack is not being treated as terror-related and no one else is believed to be connected to the incident. There is no wider threat to the public. 

Police are asking for witnesses or anyone with information on the incident to come forward.

Patients were taken to Alder Hey Children’s Hospital, Aintree University Hospital and Southport and Formby hospital.

Alder Hey Children’s declared a “major incident” Monday, saying “our emergency department is currently extremely busy,” while noting that the hospital was working with other emergency services to respond to the incident. 

The attack happened at the Hope of Hart children’s club, the BBC reported, citing journalist Tim Johnson of the local news outlet, Eye on Southport.

U.K. Prime Minister Keir Starmer called the Southport incident “horrendous and deeply shocking news.”

“My thoughts are with all those affected,” he wrote on X. I would like to thank the police and emergency services for their swift response. I am being kept updated as the situation develops.”