Oscar Pistorius is to undergo a month of psychiatric tests after the judge at his murder trial ordered a lengthy adjournment.

Olympian and Paralympian runner Pistorius was ordered to report to one of the South Africa's top mental health institutions, Weskoppies Psychiatric Hospital in Pretoria.

He will spend up to 30 days there as an outpatient while three experts – including one appointed by his defence team, test his mental health.

They will look to decide whether the 27-year-old was suffering from a condition which meant he cannot be held responsible for gunning down girlfriend Reeva Steenkamp on Valentine's Day last year.

Prosecutor Gerrie Nel – who is trying to have Pistorius convicted of murder, has claimed previously that concerns about his mental health are a "fall-back" tactic by his defence team to undo damage he did to his defence during appearances at the witness stand.

The state of the fallen star's mental health was raised by a witness for the defence, who told North Gauteng High Court Pistorius had 'generalised anxiety disorder.'

It was Nel who pushed hard for this claim to be examined by experts and now both sides wait upon the results from Weskoppies, due in a month's time.

Judge Thokozile Masipa adjourned the trial until June 30.