The 27-year-old will spend up to a month visiting the Weskoppies hospital in Pretoria after the judge in his murder trial ordered he be admitted as an outpatient.

Thokozile Masipa accepted the prosecution's request for the mental health evaluation last week, after psychiatrist Merryll Vorster said the athlete has generalised anxiety disorder.

He is accused of the premeditated murder of his 29-year-old girlfriend Reeva Steenkamp on February 14 last year.

Pistorius denies deliberately killing the model and law graduate, insisting he thought there was an intruder in his Pretoria home when he shot four times through a locked toilet door.

Psychiatrist Vorster had told the court last week that the Paralympic champion is a "distrusting and guarded" person who is "hyper-vigilant" about security.

He was pictured on his phone as he was driven in to the hospital grounds this morning.

A heavy police contingent reportedly stopped journalists from entering the grounds.

Pistorius must attend the hospital every weekday until 4pm local time, or when "formally excused".

His period of evaluation will depend on how long the four mental health experts need to compile a report for the court.