Judge Thokozile Masipa said the athlete must attend Pretoria's Weskoppies hospital, one of South Africa's top psychiatric institutions, as an outpatient for up to 30 days from May 26.  

The trial has been adjourned until June 30 while the tests are carried out.

The athlete must stay at the clinic every weekday until 4pm starting next Monday.

Ms Masipa's order instructed that: "A psychiatrist appointed ... enquire into whether the accused by reason of mental illness or mental defect was at the time of the commission of the offence criminally responsible for the offence as charged, whether he was capable of appreciating the wrongfulness of his act, or acting in accordance with an appreciation of the wrongfulness of his act."

Oscar Pistorius with his late girlfriend Reeva Steenka

She ruled that Pistorius will be allowed to leave the facility in the South African capital each day at 4pm, or when "formally excused" by hospital authorities.

His period of evaluation will be for no more than 30 days, the judge said, and will depend on how long a panel of four mental health experts needs to compile a report for the court.

Pistorius stood in the Pretoria courtroom with his hands crossed in front of him and looked at the judge as she explained her decision.

Last week, the judge ruled that Pistorius' state of mind when he shot dead his girlfriend Reeva Steenkamp should be assessed.

The ruling came after a psychiatrist giving evidence in the athlete's defence told the court he suffered from generalised anxiety disorder and that this may have influenced his judgement.

The tests were requested by the chief prosecutor and opposed by Pistorius' lawyer.

Pistorius shot Ms Steenkamp through a toilet door at his home on February 14 last year and insists he thought she was an intruder.