Neighbours of Oscar Pistorius heard arguments, gunshots and a fading scream on the night his girlfriend Reeva Steenkamp was found dead in his apartment, a court in South Africa has heard.

On the second day of the murder trial of the Olympic athlete, Michelle Burger told the court of the shots and then the fading scream from Pistorius' Pretoria home on Valentine's Day last year. 

Another neighbour, Estelle van der Merwe, told the court in Pretoria that she heard what sounded like an argument on the day Steenkamp died.

"From where I was sitting it seemed like two people were having an argument but I couldn't hear the other person's voice," she said through an Afrikaans language interpreter.

Steenkamp was declared dead at the scene with wounds to the head, arm and hip from three bullets from a 9mm handgun.

Lead defence lawyer Barry Roux read out details from her post-mortem examination report, including that "some fragments of the bullet" were removed from the 29-year-old's head.

Roux also doubted Burger's evidence, saying that Steenkamp would have "dropped immediately" due to a bullet in the head.

Burger became tearful following an exchange with Roux, who suggested she had mistaken the screams of an agitated Pistorius for that of a woman.

Pistorius, who was present for the evidence, pleaded not guilty on Monday, saying he mistook Steenkamp for an intruder.

Judge warns media

The judge warned the media to behave after a local television station leaked a photo of the state's first witness, who had asked that her image not be broadcast.

Thokozile Masipa ordered an investigation after broadcaster eNCA showed a photo of Burger during the audio broadcast of her second day of evidence.

A previous court order had ruled witnesses must give their consent to be filmed.

"I am warning the media, if you do not behave, you are not going to be treated with soft gloves by this court," Masipa, herself a former journalist, said when the court resumed.