A 12-year-old boy on Monday admitted throwing a missile at a police van during far-riot inspired riots after a knife attack in a northern England town that killed three young girls.

District Judge Joanne Hirst said the boy -- who cannot be named due to his age -- had been more involved in the violence than any other accused person she had seen "coming through these courts, adult or child".

The boy pleaded guilty to two charges of violent disorder at a court in Manchester, northwestern England.

The violence, blamed by officials on the far right, came after misinformation spread about the alleged perpetrator of a mass stabbing on July 29 at a Taylor Swift-themed dance class led to rioting in English towns and cities.

Prosecutors said the boy was part of a group that gathered two days later outside a Manchester hotel housing asylum seekers.

He was remanded to local authority custody and will be sentenced on September 2.