Philippine President Rodrigo Duterte on Monday described the police force prosecuting his deadly crime war as "corrupt to the core", but extended the crackdown until the last day of his term in 2022.

Duterte announced he intended to "cleanse" the police force, after a series of scandals in which officers were caught committing murder, extortion and robbery while using the drug war as cover.

"You policemen are the most corrupt. You are corrupt to the core. It's in your system," Duterte told reporters as he railed against the anti-drug officers who allegedly masterminded the murder of a South Korean businessman inside national police headquarters.

Duterte said nearly 40 percent of the police force engaged in illegal activities.

His comments came seven months after he took office and immediately tasked police with being the frontline troops in his plans to wipe out the illegal drug trade that he said was threatening to turn the Philippines into a narco state.

Since then, police have reported shooting dead more than 2,500 people they have accused of being drug suspects, alleging on every occasion they had to open fire in self defence.

Human rights groups and relatives of some of the victims have alleged police frequently shoot dead defenceless people, and often plant drugs and a gun on the bullet-riddled corpse.

Nearly 4,000 other people have died in unexplained circumstances in the crackdown, according to official figures.

Many of those victims have had signs placed on them labelling them drug traffickers or users.

Duterte won the presidential elections largely on a law-and-order platform headlined by a vow to eliminate the illegal drug trade in three to six months.

He promised that 100,000 people would be killed and so many bodies would be dumped in Manila Bay that the fish there would grow fat from feeding on them. 

- Drug war extended -

Once in office Duterte extended the timeframe of the drug war until March of this year, but on Monday he said there would be no end while he was in power.

"I will extend it to the last day of my term," Duterte said.

"March no longer applies."

In the Philippines, presidents are allowed to serve only a single term of six years.

Following Duterte's comments at a press conference just after midnight, national police chief Ronald Dela Rosa announced that all anti-drug units across the country would be suspended as the cleansing took place.

However critics questioned the sincerity of Duterte's outrage against corrupt police, and why the police had been given such a free hand so far to kill in the name of the drug war if he knew so many were corrupt.

"How can a corrupt and fascist police force, where impunity is the norm, successfully stamp out criminal activities such as the illegal drug trade," said Renato Reyes, secretary general of BAYAN, a coalition of leftist activist groups.

"The body count will continue to rise and more criminals in uniform will wreck havoc on the people."

Duterte, a firebrand lawyer, repeatedly told police during the election campaign and after assuming the presidency that he would shield them from prosecution if they killed people as part of the crime war.

He also told police at Dela Rosa's birthday party this month he would tolerate them engaging in illegal activities to earn "sideline" money, as long as that did not involve drugs.

"Go into smuggling, just don't do drugs," Duterte said.

Duterte said at the party he sympathised with the police for getting such low salaries, and he understood that they needed to get more income from other ways.

"I mean I'm not saying that we have to do illegal things. What I'm saying is that until such time that we (the government) can give you more and somebody offers to help, take it," he said.

Source: AFP