Two children have been killed and nine children injured in a “ferocious” mass stabbing at a Taylor Swift-themed dance class in the United Kingdom.

A 17-year-old boy was arrested on suspicion of murder and attempted murder following the incident at Southport, northwest England, at about 11.50am on Monday (UK time).

Merseyside Police Chief Constable Serena Kennedy said when officers arrived on scene they were “shocked” to see children suffering serious injuries.

The yoga and dance workshop was reportedly held in a former warehouse building on a back street.

Six of the injured children remain in a critical condition, as do two adults who were stabbed while trying to protect the young ones.

Kennedy told a press conference it was a “ferocious attack”.

“It is understood that the children were attending a Taylor Swift event at a dance school when the offender armed with a knife walked into the premises and started to attack the children,” Kennedy told a press conference.

“We believe that the adults who were injured were bravely trying to protect the children who were being attacked.

“As a mum of two daughters, and the nana 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”.

Forensic officers comb the crime scene in Southport, northwest England. Photo: Getty

UK Prime Minister Sir Keir Starmer offered his condolences and said the grief and trauma being experienced was “impossible to imagine”.

“The events today are just truly awful and I know the whole country is deeply shocked about what they’ve seen and what they’ve heard,” he said.

“I know I speak for everyone in the whole country in saying, our thoughts and condolences are with the victims, their families, their friends and the wider community.”

Armed police arrested the suspect and seized a knife after being called to the “major incident” at Meols Cop High School on Hart Street.

Alder Hey Hospital declared a major incident and asked parents not to bring their children to the emergency department unless it was urgent.

Colin Parry, owner of Masters Vehicle Body Repairs on Hart Street, who called the police, said it was “like a scene from a horror movie”.

“The mothers are coming here now and screaming.

“It’s like something from America, not like sunny Southport.”

A local parent, who did not wish to be named, said his daughter was “traumatised” by the attack.

He said: “My daughter was in it and she was traumatised.

“She ran away and she’s safe.”

A police officer receives flowers to lay at the scene. Photo: Getty

Merseyside Police said: “There are a number of reported casualties and more details will be confirmed when possible.

“Armed police have detained a male and seized a knife. He has been taken to a police station.

“Please avoid the area while we deal with this incident. There is no wider threat to the public.”

Southport MP Patrick Hurley said he was “deeply concerned” by the reports.

“I am hoping for the best possible outcomes to the casualties affected,” he wrote in a statement on X.

NWAS said it had dispatched 13 ambulances along with specialised resources of its Hazardous Area Response Team (Hart), an air ambulance and doctors.

-with AAP/AP