Taylor Swift says she is "at a complete loss" after a mass stabbing at a Swift-themed class in the U.K. left three children dead.

A 9-year-old girl "died in hospital in the early hours" of Tuesday morning, Merseyside Police said in a news release. The two children who died Monday were 6 and 7 years old.

The stabbing, which left 10 other people injured, took place in Southport, U.K., on Monday.

"The horror of yesterday's attack is washing over me continuously and I’m just completely in shock," Swift wrote on her Instagram story early Tuesday.

"The loss of life and innocence, and the horrendous trauma inflicted on everyone who was there, the families, and first responders," Swift continued. "These were just little kids at a dance class. I am at a complete loss for how to ever convey my sympathies to these families."

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Of the 10 injured, eight are children and two are adults, both of whom are in critical condition.

Five of the injured children "are in a critical condition," Tuesday's police statement said. "All those injured have suffered stab wounds sustained during the attack. Two adults are also in a critical condition after being injured during the incident," Merseyside Police Chief Constable Serena Kennedy said Monday in a statement shared with USA TODAY.

A 17-year-old male was arrested on suspicion of murder and attempted murder, Kennedy said, noting that he will be interviewed by detectives. The suspect is from the nearby coastal village of Banks and originally from Cardiff in Wales.

Police warned of misinformation regarding the arrest: "A name has been shared on social media in connection with the suspect in the incident in Southport. This name is incorrect and we would urge people not to speculate on details of the incident while the investigation is ongoing."

3 children dead, 10 injuredin mass stabbing at Taylor Swift-themed class in Southport

Police were called to reports of a stabbing at 11:47 a.m. at an address in the seaside town of Southport in Merseyside, England.

"When they arrived they were shocked to find that multiple people, many of whom were children, had been subjected to a ferocious attack and had suffered serious injuries," Merseyside Police Chief Constable Serena Kennedy said Monday in a statement shared with USA TODAY.

"It is understood that the children were attending a Taylor Swift event at a dance school when the offender, who was armed with a knife, walked into the premises and started to attack those inside," the statement continued. "We believe that the adults who were injured were trying to protect the children at the time they were attacked."

The international leg of Swift's Eras Tour will arrive in Poland on Thursday, with the singer's return to the U.K. currently set for next month.

King Charles, Prince William, Princess Kate react to Southport stabbing: 'Utterly horrific'

British royals are reacting to the mass stabbing in Southport, U.K., with King Charles III calling the incident "utterly horrific."

"My wife and I have been profoundly shocked to hear of the utterly horrific incident in Southport today," the king said in a statement shared Monday on the royal family's X account. "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."

Prince William and Princess Kate also shared their condolences to the victims' families in an Instagram story post shared Monday.

"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," the couple said in a joint statement. "We send our love, thoughts and prayers to all those involved in this horrid and heinous attack."

Swifties band together to support stabbing victims

Swift fans appear to be banding together to support victims in the Southport tragedy.

A "Swifties for Support" fundraiser appeared on Just Giving on Monday to benefit Alder Hey Children's Hospital in Liverpool, United Kingdom.

The organizers appear to be from U.K. and European fan Facebook groups. As of Tuesday morning, they have raised over £76,000 (nearly $100,000).