A South African judge is set to rule on whether to grant a state appeal opening the way for Oscar Pistorius to serve more time behind bars.

Prosecutors launched the process after Judge Thokozile Masipa sentenced the Paralympic gold medallist to five years' jail in October over the shooting death of his girlfriend Reeva Steenkamp.

Pistorius admits shooting Steenkamp four times through a locked toilet door on Valentine's Day 2013. He told the court he thought she was an intruder.

The judge found him guilty of culpable homicide rather than a more serious charge of murdering Steenkamp.

Prosecutor Gerrie Nel argued in appeal papers filed last month that Masipa misinterpreted the law when she ruled Pistorius did not intentionally shoot Steenkamp, describing the sentence as "shockingly light" and "inappropriate".

Pistorius, who became famous after competing as a double amputee against able-bodied runners in the Olympics, can qualify for house arrest after serving 10 months of his sentence behind bars.

The hearing is expected to take two hours. Should Masipa grant the appeal, the case will be heard in South Africa's Supreme Court of Appeal in Bloemfontein.

Law expert Mannie Witz said Pistorius could get bail if the state succeeds in its application, the South African Press Association reports.

But the judge may not necessarily grant the appeal, siding with defence lawyers representing the athlete who say her interpretation of the law was correct.

If Masipa refuses to grant the appeal, the state can petition the decision.

"I honestly don't think Masipa would refuse leave to appeal, there's just too much controversy about the judgment," said Martin Hood, a criminal lawyer based in Johannesburg.

"It doesn't matter what the outcome of the appeal is, if the appeal is allowed then other judges will be able to comment on the decision, and that's critical," Hood said.