Oscar Pistorius attends his trial at the high court in Pretoria. REUTERS/Themba Hadebe/Pool

Pretoria - A distraught Oscar Pistorius said on Tuesday he did not immediately realise what he had done after he fired the shots that killed his girlfriend Reeva Steenkamp.

He was testifying in the High Court in Pretoria, where he is on trial for murder.

Pistorius said that after shuffling into the bathroom and firing off four shots very quickly, he still thought he was dealing with an intruder.

He shouted to Steenkamp to call the police.

He has been charged with murdering her on Valentine's Day 2013, but he said he mistook her for an intruder when he shot her dead.

Pistorius said at this stage, he was still scared to retreat because he was not sure if somebody was trying to enter his home with a ladder or if someone was in the toilet.

“I don't know how long I stood there for, shouting for Reeva...,” said Pistorius.

His ears were ringing and he could not hear if there was a response or not. He walked to the room, still shouting to Steenkamp.

“I didn't hear anything,” he said.

It did not occur to him that it could be Steenkamp in the toilet and still thought it could be intruders on ladders trying to get up to the first floor.

He got to his bed, and was still talking to Steenkamp.

“But there was nobody, no one responded to me,” he said, choking up.

He put his hand to the right side of the bed to see if Steenkamp was there.

He thought she had got down to the floor as he had told her to when he first heard a noise.

He was still holding his firearm towards the passage, with not much light available.

“I then...it was that point My Lady that it first dawned upon me that it could be Reeva that could be in the bathroom in the toilet.”

He jumped up and ran his hand behind the curtain to see if she was not hiding behind there.

He made his way back up the bathroom passage on his stumps with “mixed emotions”, not wanting to believe it could be Steenkamp in the toilet.

He tried to open the toilet door but it was locked. He ran to the balcony and screamed “help, help, help”.

His put his prosthetic legs on, ran as fast as he could and tried to kick the door.

He panicked, was screaming, crying out.

“I don't think I ever screamed like that or cried like that. I was crying out for the Lord to help me, I was crying for Reeva I was screaming.”

When he got the door open he saw Steenkamp and she was not breathing.

When he said this he doubled over and howled and sobbed.

Court was adjourned until Wednesday at 9.30am.

Pistorius has denied that he murdered Steenkamp and two other charges related to the Firearms Act.

Earlier, he admitted that he was holding a firearm when it was discharged at Tasha's in Melrose Arch although he has pleaded not guilty to that charge too.

The other Firearm Act charge relates to firing a gun out of the sunroof of a car in Modderfontein. He denied this.