A self-declared white supremacist pleaded guilty Monday to shooting dead 10 Black people during a racist, live-streamed, rampage at a supermarket in the US state of New York earlier this year, AFP reported.

Payton Gendron, 19, will spend the rest of his life in prison after admitting one state charge of domestic terrorism motivated by hate over the massacre in Buffalo in May.

Erie County District Attorney John Flynn said Gendron had pleaded guilty to all charges, including 10 counts of murder in the first degree and three attempted murder charges.

"While justice has been accomplished, nothing will ever bring back the 10 beautiful people who lost their lives on that day," Flynn told reporters.

"Hopefully the legal closure will provide the families and the victims some measure of relief," he added.

Gendron had planned the attack for months, targeting Tops Friendly Market in Buffalo because of its large surrounding African-American population.

He drove from his hometown of Conklin, more than 200 miles (322 kilometers) away, with the intention of killing as many Black people as possible, prosecutors said.

Wearing heavy body armor and wielding an AR-15 assault rifle, Gendron shot four people in the store's parking lot, three of them fatally, before entering the supermarket.

Among those killed inside was a retired police officer working as a security guard. He fired several shots at the assailant before being shot himself, police said.

Gendron wore a helmet with a video camera attached and live-streamed the attack on the platform Twitch.

He is the first person in New York to be convicted of the state's domestic terrorism charge, which was introduced in 2020. It carries a penalty of life without parole.

Gendron still faces federal hate crime charges that could see him receive the death penalty.

He had initially pleaded not guilty to a single count of first-degree murder before state authorities later added the other charges.