A gunman who killed 23 people at a Walmart in Texas four years ago after posting an online rant about a "Hispanic invasion" has pleaded guilty.

Patrick Crusius, 24, admitted 90 federal counts, including hate crimes and firearms charges.

He drove 11 hours to the store in the border city of El Paso on 3 August 2019 to spray shoppers with bullets after posting his hate-filled screed online.

It is one of the deadliest mass shootings in US history.

The shackled gunman looked impassive as he entered his plea during Wednesday's hearing in El Paso, according to court reporters.

He changed his plea to guilty after federal prosecutors said they would not seek the death penalty.

He could still face the death penalty if he is later convicted on a state capital murder charge.

Albert Hernandez, who lost his sister and brother-in-law in the shooting, told KFOX14 TV station: "Of course he's pleading guilty because he wants to save his own skin."

The gunman admitted leaving his home near Dallas to go to the border town, which is 80% Hispanic, with a semi-automatic rifle and rounds of ammunition to target Latinos.

Eight of those killed held Mexican citizenship.

More than two dozen other people were injured in the attack, which unfolded on a busy weekend in August.

The gunman had shared his screed to the now-defunct 8chan website about 20 minutes before the attack.

He bought the rifle used in the massacre together with 1,000 rounds of ammunition weeks beforehand.

US Attorney General Merrick Garland noted in a statement that the killer described himself as a "white nationalist".

"Today's action makes clear that the justice department will not tolerate hate-fuelled violence that endangers the safety of our communities," said Mr Garland, the nation's top law enforcement official.

The trial was set to take place next year, but because the gunman pleaded guilty, sentencing could go ahead later this year, the judge said.

The gunman's lawyer said his client had long planned to plead guilty.

"He's glad that it's finally done," said Joe Spencer. "There are no winners in this case. He's going to be serving 90 consecutive life sentences."