A white gunman who shot and killed 10 people in a racially motivated attack in Buffalo, New York has pleaded guilty to murder and terrorism charges.

The plea means he will be sentenced to life in prison without parole. New York does not have the death penalty.

The 19-year-old killer initially pleaded not guilty to the state charges in June.

"I understand this is a momentous and tremendously emotional event," Judge Susan Eagan said in court on Monday.

The judge named each victim and asked the gunman if he had killed them because of their race. He showed little emotion as he said "yes" to each charge.

The charges include first-degree murder, murder as a hate crime, and domestic terrorism motivated by hate.

The gunman is also facing multiple federal charges over the 14 May shooting which could be punished with the death penalty.

The attack happened after the gunman drove more than 320km (200 miles) to a predominantly black neighbourhood in Buffalo, New York's second-largest city.