Paralympic champion Oscar Pistorius has told the High Court in Pretoria that his mother had a number of "security concerns" when he was a child growing up.

The 27-year-old has been testifying for the first time during his trial for murder, where he is accused of killing girlfriend Reeva Steenkamp on Valentine's Day last year.

The double amputee, whose mother died when he was 15 years old, shot dead the South African model by firing four gunshots through a bathroom door at his home in Pretoria.

"My mother had a lot of security concerns," Pistorius told the court. "We grew up in a family where my father wasn't around much, she would often get scared at night, she would phone the police.

"My mother had a pistol. She kept her firearm in a padded bag under her pillow."

Pistorius denies murder by maintaining that he mistook Steenkamp for an intruder when he fired the shots.