One of the first people on the scene after Oscar Pistorius shot girlfriend Reeva Steenkamp feared the athlete would kill himself, a court has heard.

Giving evidence on Thursday, Johan Stipp said he entered the athlete's home, minutes after hearing screams and shots, to find Pistorius kneeling over the lifeless body of a woman.

"I shot her. I thought she was a burglar and I shot her," Stipp quoted the 27-year-old as saying.

Stipp, a doctor, went on to describe his futile attempts to revive Steenkamp, a 29-year-old model and law graduate who had been dating Pistorius for a few months.

She died on February 14 last year after being hit by three bullets, including one to the head, out of four fired by Pistorius through the locked door of an upstairs toilet.

He denies murder, arguing that he thought she was an intruder.

Stipp told the court Pistorius begged him to save Steenkamp's life.

"Oscar was crying all the time. He prayed to God: 'Please let her live, she must not die'," he said.

Stipp and Pistorius were joined by the building manager, Johan Stander.

Stipp told the court he feared Pistorius might kill himself when he left Steenkamp's body to go upstairs. 

"I noticed that Oscar was going upstairs and I asked Mr Stander if he knew where the gun was because it was obvious that Oscar was emotionally very, very upset," he said.

"I didn't know the situation in the house so I thought maybe he was going to hurt himself."

Pistorius sat slumped in the dock, his head bowed and his hands covering his ears.

The case continues.

Source: Reuters