Reducing convicted murderer Oscar Pistorius' sentence from the prescribed 15-year minimum to six "induces a sense of shock", the High Court in Johannesburg heard on Friday.

Judge Thokozile Masipa did not have a "clean slate" when sentencing the former Paralympian for the murder of Reeva Steenkamp, prosecutor Gerrie Nel told her.

She should have taken as her starting point the prescribed minimum sentence.

"A severe, standardised and consistent response from the court is required," said Nel, referring to the sentencing of offenders for serious crimes.

Nel was arguing for leave to appeal Masipa's 6-year sentence, which she imposed on Pistorius on July 6.

Claiming he thought there was an intruder in his bathroom should not be considered a mitigating factor. An intruder's life could not be considered to be less important than Steenkamp's, Nel submitted.

In the early hours of February 14, 2013, Pistorius shot Steenkamp four times through the locked door of the toilet in his Silver Woods Country Estate home. He claimed he thought there was an intruder behind the door about to emerge and harm him, and that Reeva was still in bed.