THE racist white gunman who targeted a supermarket in a mainly black neighbourhood of Buffalo, New York State in the United States earlier this year was set to plead guilty today to the mass murder of 10 people and wounding three others, according to lawyers.

Payton Gendron, aged 19, was scheduled to appear at Erie County Court for a hearing.

According to the attorneys representing those killed and injured, the shooter intended to plead guilty on all counts and to waive his right to an appeal.

The 25-count grand jury indictment includes charges of murder, murder as a hate crime and domestic terrorism motivated by hate, which carries an automatic life sentence upon conviction.

Mr Gendron also faces separate federal hate crimes charges that could result in a death sentence if he is convicted. 

The white supremacist reportedly drove for three hours to Buffalo from his home in Conklin, New York, intending to kill as many black people as possible at the Tops Friendly Markets supermarket, which he chose because of its location in the predominantly black East Side neighbourhood.

Shortly before opening fire with an AR-15-style rifle on May 14, he posted documents online outlining his racist views and revealed that he had been planning the attack for months. 

Mr Gendron live-streamed the attack from a helmet-mounted camera as he shot store employees and shoppers. He was arrested in the car park.

Relatives of the victims have since called on Congress to address issues of white supremacy and gun violence. 

The store was closed for two months after the attack. A food summit organised by Buffalo-based attorney and activist Kevin Gaughan last month focused on closing the “grocery gap” laid bare by the attack on the neighbourhood’s only supermarket.