Police say a third child is dead after a 17-year-old boy went on a stabbing spree at a Taylor Swift-themed dance class for young children in the United Kingdom on Monday. 

The girl, aged 9, died of her injuries early Tuesday, the BBC reported. Five other children and two adults remain in critical condition at local hospitals.

Swift said she was "completely in shock" and still processing "the horror" of the attack.

"These were just little kids at a dance class," she wrote in an Instagram story. "I am at a complete loss for how to ever convey my sympathies to these families." 

UK STABBING SPREE LEAVES 2 KIDS DEAD, 9 OTHERS INJURED AT TAYLOR SWIFT-THEMED EVENT: ‘DEEPLY SHOCKING’

Flowers were left for the victims of the dance class stabbing attack

Floral tributes near the scene in Hart Street, Southport, Britain, on July 30, 2024, where two children died and nine were injured in a "ferocious" knife attack during a Taylor Swift event at a dance school on Monday. A 17-year-old male from Banks, Lancashire, has been arrested on suspicion of murder and attempted murder over the incident. (James Speakman/PA via AP)

The 17-year-old suspect was arrested on suspicion of murder and attempted murder. Investigators are working to determine a motive in the rampage in Southport in northwest England. 

Local people left flowers and stuffed animals in tribute at a police cordon on the street lined with brick houses in the seaside resort near Liverpool — nicknamed "sunny Southport" — whose beach and pier attract vacationers from across northwest England.

Taylor Swift points to the crowd in a sparkly pink outfit during the Eras Tour

Pop sensation Taylor Swift said she was "completely in shock" and still processing the knife attack at a dance class in the United Kingdom.  (Marcelo Endelli/TAS23/Getty Images for TAS Rights Management)

Witnesses described scenes "from a horror movie" as bloodied children ran from the attack just before noon on Monday. The suspect was arrested soon after on suspicion of murder and attempted murder. Police said he was born in Cardiff, Wales, and had lived for years in a village about 3 miles from Southport. He has not yet been charged.

Police said the attack is not being treated as terror-related, and they are not looking for any other suspects. 

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Police work at the scene in Southport, England, where a man has been detained and a knife has been seized after a number of people were injured in a reported stabbing on Monday, July 29.

Police work at the scene in Southport, England, where a man has been detained and a knife has been seized after a number of people were injured in a reported stabbing on Monday, July 29. (Left: Robert Kamau/GC Images; Background: )

"We believe the adults who were injured were bravely trying to protect the children who were being attacked," Merseyside Police Chief Constable Serena Kennedy said, according to the Associated Press. 

The attack happened at the Hart Space, a local community center. The suspect targeted a Taylor Swift-themed yoga and dance workshop for children ages 6-11.

Witnesses described hearing screams and seeing children run from the scene covered in blood. 

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Emergency vehicles in Southport, England

Emergency services are seen responding Monday to the stabbing spree in Southport. (James Speakman/PA via AP)

"They were in the road, running from the nursery," said Bare Varathan, who owns a shop nearby. "They had been stabbed, here, here, here, everywhere," he said, indicating the neck, back and chest.

The dance teacher, identified as Leanne Lucas, has been praised for her bravery after desperately trying to protect the children during the attack, according to The Independent. She is reported to be one of the two adults in critical condition. 

U.K. Prime Minister Keir Starmer called the stabbing spree "horrendous and deeply shocking."

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

Prince William and his wife Catherine said that "as parents, we cannot begin to imagine what the families, friends and loved ones of those killed and injured in Southport today are going through."

Fox News Digital's Greg Norman and the Associated Press contributed to this update.