A witness in the murder trial of Oscar Pistorius has claimed in court that she heard a woman 'scream terribly' from the Paralympian's home on the night that his girlfriend was shot dead.

The 27-year-old has pleaded not guilty to the murder of Reeva Steenkamp, who was shot dead through a bathroom door at his home in Pretoria on Valentine's Day last year.

The first witness of the trial, which began in South Africa today, has been named as Michelle Burger, who is a neighbour of Pistorius and a university teacher.

According to The Mirror, she told the court that she awoke at 3am on February 14, 2013 to "terrible screams" from a woman, and ordered her husband to call security after she heard a woman scream for help and a man scream for help three times.

The witness, who revealed that she heard gunshots being fired, told the court that she wanted her husband to tell security that "people were being attacked".

"I heard the woman's screams again," the newspaper quotes Burger as saying. "It was worse - it was more intense. It was a climax. She was very scared.

"Just after her screams I heard four shots. It was four gunshots. The time between first and fourth was much longer than between second and third."

Pistorius has maintained that he mistook Steenkamp for an intruder when he fired the shots.