He was held on suspicion of murder and attempted murder. Nine other children were wounded, six of them critically, and two adults were in critical condition.

“We believe that the adults who were injured were bravely trying to protect the children,” said Chief Constable Serena Kennedy from Merseyside Police.

She said emergency services arriving at the scene found “multiple people, many of whom were children, had been subjected to a ferocious attack and had suffered serious injuries.”

An advertisement posted online described the event as a yoga and dance workshop for children aged between six and 11.

Merseyside Police said the motive for the attack was unclear but it was not believed to be terrorism-related and they were not looking for anyone else in connection with the stabbings.

Police said armed police had arrested the suspect and seized a knife after being called around 11:50am (1050 GMT) to an address in Southport, north of Liverpool.

The arrested teenager is from Banks, a village not far from Southport, they added.

“At this early stage, enquiries are ongoing to establish the motive for this tragic incident and we would urge people not to speculate,” police said.

North West Ambulance Service said it had treated eight patients with stab injuries who had been taken to three different hospitals, including Alder Hey Children’s Hospital.

The hospital said it had declared a major incident and its emergency department was extremely busy. It asked parents only to bring in their children if it was urgent.

“Horrendous and deeply shocking news emerging from Southport. My thoughts are with all those affected,” Prime Minister Keir Starmer said 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.”