Two children killed and nine injured in stabbing attack at Southport ...

Two children have been killed and another nine injured in a stabbing attack at Southport, on England's north-west coast.

Police have arrested a 17-year-old boy in connection with the attack, and say they are not looking for any other suspects.

Police say the boy has been detained on suspicion of murder and attempted murder. However, is yet to be charged.

Two children have been killed and nine injured during a stabbing attack in England's north-west that one witness has likened to a "horror movie".

Warning: This story contains distressing details.

A 17-year-old boy has been arrested in connection with the incident, which took place at a Taylor Swift-themed dance and yoga class for primary school children in the town of Southport shortly before midday on Monday, local time.

Of the nine injured children, six are in a critical condition while three have serious injuries. Two adults are also in a critical condition.

Police and paramedics were called to a street in the seaside town, about 30 kilometres north of Liverpool, at 11:47am.

"They were shocked to find multiple people, many of whom were children, had been subjected to a ferocious attack and had suffered serious injuries," Chief Constable Serena Kennedy said.

She said the offender had walked into a dance class and started attacking those inside.

"As a mum and a grandmother, I can't begin to imagine the pain and suffering the families of the victims are going through," Chief Constable Kennedy said.

A police officer surveys the area where several children were stabbed on Monday.(PA: James Speakman via AP)

The injured have been taken to three different hospitals in the area.

Chief Constable Kennedy said the 17-year-old boy from a nearby village had been arrested "on suspicion of murder and attempted murder". He is yet to be charged.

She said the adults had been injured while "bravely trying" to protect the children.

The attack took place at a community centre on Hart Street called The Hart Space.

A social media post advertising the two-hour Taylor Swift-themed event said it was a "yoga, dance and bracelet making workshop" that was open to children aged six to 11.

The British summer school holidays began only last week.

Colin Parry, who owns a business nearby, told the BBC he called the police after seeing young girls bleeding.

"Ambulances started arriving then. It was just mayhem," Mr Parry said.

"It's the worst thing I've ever seen in my life … it is like a scene from a horror movie."

Mr Parry also described mothers racing to the scene "wailing and screaming".

Local coffee shop owner Bare Varathan told the Manchester Evening News he saw seven to 10 bleeding children outside the building.

"They were all aged about 10," he said. "One of them was really seriously injured."

King Charles III released a statement saying he and Queen Camilla were "profoundly shocked" to learn of the "utterly horrific" incident.

"We send our most heartfelt condolences, prayers and deepest sympathies to the families and loved ones of those who have so tragically lost their lives, and to all those affected by this truly appalling attack."

Tonia Whewell lives on the street next to where the deadly attack took place.(ABC News: Isabella Higgins)

Tonia Whewell, who lives on the street next to where the incident took place, said she was still in "a state of shock".

"It's just horrific the thought of children being stabbed in the summer holidays … how do you comprehend that?

"You just can't begin to fathom how the parents are feeling tonight."

She said the seaside community she had been a part of for 28 years would "never get over it".

"How can we move on from something like this?" she said.

David Farrah and his son went to Hart Street to lay flowers after learning of the attack.(ABC News: Isabella Higgins)

Another local, David Farah, said the incident had put everyone in the town on high alert.

"Initially it was just panic, what's going on, are we safe, who is out there … then it's just shock," he said.

He took his son to lay flowers at Hart Street.

"This is one of those things you'd never expect to happen in your own little town," he said.

Firefighters were the first on the scene to offer first aid and trauma support.

At least 13 ambulances were deployed, as well as an air ambulance crew.

Dave Kitchin, from the North West Ambulance Service, described the scene as "devastating".

"No doubt this incident will have a lasting impact on the whole community, and our thoughts are very much with them," he said.

A police officer places flowers, given by residents, at the scene of the attack on Monday.(Reuters: Temilade Adelaja)

"However … the investigation is not being treated as terrorist-related."

British Prime Minister Keir Starmer said the events in Southport were "truly awful" and "the whole country is deeply shocked".

He added that it was "almost impossible" to imagine the grief of those affected by the attack and he thanked the emergency responders for their professionalism.