A white teenage boy told his mother he "snapped" just before he was arrested by police for opening fire on a South African squatter camp, killing a baby, a young boy, and two adults.

"Mom, something just snapped inside me," 18-year-old Johan Nel reportedly told his mother Corrie just before he was arrested by South African police for the incident.

Nel allegedly shouted the derogatory term "kaffir, kaffir, kaffir" as he began shooting his .303 rifle at the Swartruggens camp, 100 miles west of Johannesburg.

His victims included a three-month-old baby, a 10-year-old boy, a 30-year-old man, and a woman who died 24 hours later in hospital. A further seven people suffered gunshot wounds, three seriously.

'Something just snapped': Johan Nel, with the gun he reportedly used to open fire

Nearly 100 people protested outside the Swartruggens Magistrates' Court as Nel was charged today