Two children were killed and 11 people were injured in a stabbing attack at a Taylor Swift-themed event at a dance school in the United Kingdom, police said.

The 11 injured includes nine children — six of whom are in critical condition — and two adults who are in critical condition, Merseyside police said. It appears the adults were trying to protect the children, police said.A 17-year-old boy has been arrested on suspicion of murder and attempted murder, police said.

The incident isn’t being treated as terror-related and no other suspects are being sought, police said. A motive isn’t clear, police added.

Officers responded just before noon local time to reports of a stabbing at a property on Hart Street in Southport, a seaside town about 20 miles north of Liverpool, according to Merseyside police.

Officers who arrived at the scene were shocked at the “ferocious” attack, police said.

“Horrendous and deeply shocking news emerging from Southport,” U.K. Prime Minister Keir Starmer wrote on social media. “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.”

The town of Southport sits in the county of Merseyside, in England’s northwest.