Prosecutors on Friday urged Malaysia's highest court to uphold former prime minister Najib Razak's 12-year jail sentence for corruption, saying his "dishonesty has been established".

On the second day of hearings at the Federal Court, the prosecutors pressed on with their case despite Najib's claim that he was not being given a fair trial.

Najib, 69, has mounted a high-stakes final appeal, which could see him imprisoned, or acquitted and attempting a return to power.

At the start of Friday's hearing, Najib's lead counsel Hisyam Teh Poh Teik told the court that the former leader had discharged part of his defence team.

There was a brief silence, with Najib, wearing a face mask, seen looking down.

Chief Justice Maimun Tuan Mat, however, calmly ordered the prosecution to "proceed" with their arguments.

Maimun had previously said that any delays in the proceedings were a waste of public funds, and that "justice delayed is justice denied to others".

Najib and his ruling party were voted out in 2018 following allegations of their involvement in a multibillion-dollar financial scandal at state fund 1MDB.

Najib and his associates were accused of stealing billions of dollars from the country's investment vehicle and spending it on everything from high-end real estate to pricey art.

Following a lengthy High Court trial, Najib was found guilty of abuse of power, money laundering and criminal breach of trust over the transfer of 42 million ringgit ($10.1 million) from former 1MDB unit SRC International to his personal bank account.

He was sentenced to 12 years in jail in July 2020, though he has not been sent to prison while the appeals process plays out.

An appellate court last December rejected his appeal, prompting him to mount a final challenge before the Federal Court.

Najib "had failed to cast any reasonable doubt on the prosecution case and therefore... should be convicted," government prosecutor V. Sithambaram told the court.

"The appellant’s dishonesty has been established," he said.

He added that Najib's claim that he did not know the source of the funds "is an afterthought to evade criminal liability".

Hisyam, the defence lawyer, had also asked the court on Thursday to be discharged, citing inadequate time to prepare for the case, but the judges refused.

Najib said he objected "in the strongest of terms" to how the court forced his lawyer to continue despite him wanting to be discharged, which he said effectively left him without proper counsel.

"My rights to life, liberty and right to a fair hearing is at stake," he said.

Sankara Nair, a lawyer not involved in the hearings, told AFP Friday that the actions by Najib's defence appeared meant to "frustrate the proceedings of the court".