Prison for former PNG commissioner

Papua New Guinea's former police chief has been sentenced to three years in prison after being found guilty of contempt for failing to arrest the nation's prime minister during a long running corruption probe.

In a decision hailed as a vindication of the court's authority by the chairman of PNG's anti-corruption watchdog Task Force Sweep, former police commissioner Geoffrey Vaki is expected to soon be taken into custody.

In June a PNG court found Mr Vaki guilty of contempt for failing to execute a district court arrest warrant issued last year for Mr O'Neill, and for later telling media any decision to arrest him was "a long way down the road".

Sweep chairman Sam Koim, who was in court on Friday, told AAP the sentencing vindicated the court's authority.

"To my knowledge, three years is the highest penalty for contempt ever in this jurisdiction. This is how serious the court has treated the Police Commissioner's refusal to execute the warrant of arrest on (the prime minister)," he said.

"It is sending a strong message that all persons must observe the terms of the order (warrant)."

Mr Vaki is expected to launch an appeal.

A police spokesman said he was aware of the verdict but was waiting for confirmation from the court.

The warrant for Mr O'Neill's arrest was obtained in June last year by fraud investigators who wanted to grill the prime minister over allegations he authorised the siphoning of millions of dollars in public cash to a law firm, a claim Mr O'Neill denies.

An injunction has been put on the arrest warrant, which is under challenge in a separate case.

Mr Vaki was sacked for poor performance in early May, just short of a year since he was installed in the job.

His sacking and replacement by commissioner Gari Baki marked the third change to the upper echelons of PNG's police force in four years.