Paralympic champion Oscar Pistorius is alleged to have taken acting lessons before his murder trial in Pretoria, South Africa.

The 27-year-old has been accused of killing girlfriend Reeva Steenkamp, whom he shot dead through a bathroom door at his home on Valentine's Day last year.

Jani Allan, who is a former columnist for the South African Sunday Times, claimed in an open letter to Pistorius on her blog that the double amputee had taken lessons from a "close friend" of hers.

The athlete has broken down in tears numerous times at the High Court and has also been heard retching when details of Steenkamp's injuries have been revealed.

Allan wrote: "I have it from a reliable source that you are taking acting lessons for your days in court. Your coach has an impossible task. Oscar, I look at you mewling and puking in the witness stand."

Pistorius denies murder by maintaining that he mistook the South African model for an intruder when he fired four gunshots through the door.

The trial will resume on May 5.