Philippine President Rodrigo Duterte has vowed to pursue his campaign against corruption with as much fervour as his controversial and violent anti-crime drive.

He disclosed on Tuesday that he has fired at least 92 officials for graft, including two top officials of the immigration bureau - both his fraternity brothers - who were embroiled in a payoff scandal involving a wealthy Chinese online gaming operator.

"If you are corrupt, I will fetch you with a helicopter, and I will throw you out on the way to Manila. I have done that before. Why should I not do it again?" Mr Duterte said in a speech, following a visit on Tuesday to a relief centre at a province hit by Typhoon Nock-Ten.

He alluded to having done that to a man suspected of kidnapping, raping and killing the daughter of a wealthy Filipino-Chinese couple despite payment of ransom. It was not immediately possible to confirm his claim. "You kidnap someone. You rape and then kill her, even after her parents had paid ransom. What kind of criminal are you? You deserve to be thrown out (of a helicopter)," he said.

His aides have sought to soften his controversial remarks by saying Mr Duterte is fond of "hyperboles" and embellishing his exploits .

Mr Duterte, 71, has previously admitted to killing criminal suspects.

Two weeks ago, he recounted that he emptied an entire clip of an M16 assault rifle into three men who abducted a woman on her way to a video store in 1988.

Before that, he told a group of businessmen that when he was mayor of the southern city of Davao, he would roam the streets on his motorcycles "looking for a confrontation, so I could kill".

He has insisted that he killed criminals who chose to put up a fight instead of surrendering.

While the human rights commission has investigated killings in Davao when he was mayor, he has never been formally charged, even for deaths he has claimed to have been responsible for.

Mr Duterte has been criticised for thousands of extrajudicial killings that have blighted his war on crime.

Latest available data shows more than 2,100 suspects have been killed in police operations since Mr Duterte, who won on a promise to eradicate crime and corruption, took office on June 30. Another 4,000 were believed to have been killed by vigilantes or in purges within criminal gangs.

In a letter they sent last week to the US State Department, Senators Marco Rubio, Edward Markey and Christopher Coons described Mr Duterte's anti-crime drive as "a campaign of mass atrocities".

Mr Duterte, however, has refused to stand down, calling his critics in the United States and human rights activists with the United Nations "idiots" and leaning on China and Russia for support.

The government on Tuesday claimed victory, citing a 49 per cent drop in crimes since Mr Duterte became President.

It took note of an 18 per cent rise in murders, but Mr Duterte's spokesman Ernesto Abella said this should be "put in context".

"Index crime rates have lowered significantly, telling us that the majority of those crimes have been related to drugs. So in a sense, it is a question of being able to see it with the right perspective," said Mr Abella.

"If you hear anecdotal reports of people, they actually say how much they deeply appreciate the fact that they can go home safer."