Rodrigo Duterte, the president of the Philippines, has threatened corrupt government officials by saying he would have thrown them off a flying helicopter, warning that he had personally carried out the action before and had no qualms about doing it again.

The former prosecutor and governor said that he once hurled a Chinese man suspected of rape and murder out of a helicopter.

"If you are corrupt, I will fetch you using a helicopter to Manila and I will throw you out. I have done this before. Why would I not do it again?" Duterte said during a speech to victims of a typhoon on Tuesday, a clip of which was posted later on a video feed of the president's office.

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According to police, more than 5,900 people have been killed since Duterte took office in late June and declared a war on drugs, leading to fears of mass extrajudicial killings and a breakdown in the rule of law.

Duterte's latest threat comes just a few weeks after he admitted killing people during his 22 years as a mayor of Davao city, sometimes riding a motorcycle looking for "encounters to kill".

He said those killings were part of legitimate police operations, including a hostage incident. Some senators have warned Duterte that he risks impeachment over his comments.

'They were lucky'

Duterte also said that six people arrested last week during a seizure of more than half a tonne of methamphetamine, known locally as "shabu", in the capital were fortunate he was out of town.

"They were lucky I was not in Manila that time. If I had known there were that much shabu inside a house, I would definitely kill you," he said.

"Let's not make any drama, I will personally gun you down if nobody else will do it."

It was not immediately clear when or where the helicopter incident Duterte spoke of took place.

His spokesman, Ernesto Abella, suggested it may not have actually happened.

"Let's just say, 'urban legend'," Abella said without elaborating.

Duterte has at various times claimed he killed people.

In an interview with Rappler in late 2015, before he took over the presidency, he said that he recently killed three people.

During the same period, responding to reports that "he killed 700 people," he said: "They underestimate the figures ... [I killed] around 1,700."

The UN's top human rights envoy has called for an investigation into Duterte's claims of killing people, to which Duterte last week responded by calling him "stupid", an "idiot" and a "son of a bitch" who should go back to school.