Liverpool, UK - A UK judge on Thursday sentenced a self-confessed child killer to life in custody for murdering three young girls in a frenzied stabbing spree at their summer dance class.

"I consider it likely he will never be released," Judge Julian Goose said, adding that Axel Rudakubana (18) must serve a minimum of 52 years in detention for his "extreme violence."

"The harm Rudakubana has caused to each family, each child, and to the community has been profound and permanent," the judge told Liverpool Crown Court in northwest England.

Rudakubana had admitted three charges of killing the three girls who died in the attack in Southport – Bebe King (6), Elsie Dot Stancombe (7), and Alice da Silva Aguiar (9).

He also confessed to the attempted murder of eight other children and two adults, as well as possessing a knife when he burst into a Taylor Swift-themed dance class in July last year.

And he pleaded guilty to producing a biological toxin – ricin – and possessing an Al-Qaeda training manual.

The judge said the violent attack, which Rudakubana unleashed just nine days before his 18th birthday, took just 15 minutes.

"Had he been able to, he would have killed each and every child – all 26 of them," the judge said. "He was prevented from murdering more only by the escape of other children."

After some of the injured girls escaped, Rudakubana "returned to continue his sustained and brutal violence against two of the youngest of those children, stabbing them multiple times," the judge added.