A Good Samaritan has been shot dead by a motorist he tried to help on a snowy North Carolina highway, said police.

Bullets flew after a group of people stopped to help the driver whose vehicle had slid off a road in Catawba at around 5:20pm on Friday.

When the helpers began to suspect the motorist was intoxicated they mentioned calling the sheriff's office, authorities say.

"He heard them say that," Catawba County Sheriff's Office spokesman Coy Reid told ABC News. "He jumps out of the car with a pistol."

The group ran, but one was shot and fell over.

"He shoots and hits one of them," Mr Reid said.

The suspect then "walks over and fires multiple shots into him", the sheriff's spokesman added.

The gunman, Marvin Lee, appeared to be under the influence of drugs or alcohol, according to the authorities.

He returned to the vehicle and refused to get out.

Lee was pepper-sprayed and taken into custody after a SWAT team responded with an armoured vehicle.

The Good Samaritan was named as Jefferson Heavner, 26, of Newton, reports WSCO9 News.

Lee is charged with murder and is due to appear in court on Monday.

The shooting happened as a massive blizzard with gale-force winds hit the southern and eastern US.